Harry/Ginny is one of the most divisive pairings in a fandom already heavily populated with shipping warfare. Their shippers, JKR herself amongst them, argue that Ginny and Harry are true soulmates and that "they're both very strong and very passionate. That's their connection, and they're remarkable together." (JK Rowling). Whereas, their detractors, including myself, suggest that their romance was rushed and unrealistic, that they have little serious interaction and that Harry's attraction towards her lacked foreshadowing.
Romance writing isn't necessarily JKR's forte. I love her, and she's a wonderful fantasy-adventure writer, but lacks the skills of a romance writer. However, she gets the balances of falling in love just right in her best written pairing; Ron/Hermione. (I actually always felt that Ron/Hermione were the main romance of the books, rather than Harry/Ginny, due to theirs being built up from Book One.)
To have a look at why Harry/Ginny fail where Ron/Hermione succeed, let's take a look at respective points about their romances;
Point One: Assumption, Attraction And Infatuation
Jennifer Crusie, a romance writer I greatly respect, stated in an essay that the "basic psychological progress" of romance is "assumption, attraction, infatuation and attachment [true and unconditional love] - which is why they all felt true emotionally..." Assumption and attraction are based on questioning whether a person is sexually attractive, and then becoming sexually attracted to that person. However, to move into infatuation, there must be physical and psychological cues, where two people must share intimate moments; pain, fear or great happiness. Ron and Hermione have this down to a pat; they've been involved in dozens of dangerous situations together, and often demonstrate great concern for the other's safety; the most touching example being in Deathly Hallows, when Ron hears Hermione tortured by Bellatrix Lestrange and continually screams "HERMIONE!" through the bars of his cell. This was present as early as Philosopher's Stone, where Hermione screams "NO!" as Ron plans to sacrifice himself in order for Hermione and Harry to find the Philosopher's Stone.
Unfortunately, Harry and Ginny do not experience similar tests. Once Harry has realized his feelings toward Ginny, they are engaged in few mortally dangerous situations. Harry's witnessing of Ginny's near murder at the hands of Bellatrix could count, but that scene occurs less than 50 pages before the ending of the entire series - far too late, especially for the so-called major couple.
It's possible for fans to argue that Harry and Ginny's infatuation cues begin in the Chamber Of Secrets, where they experience great pain and danger together. To an extent, this is true; Ginny is dying and terrified, and Harry rescues her from the Most Evil Wizard Of All Time yadda yadda. This episode would have been an ideal infatuation cue for Ginny and Harry. Unfortunately, their mutual attraction does not begin until several years later. Harry even has another relationship during the intervening years. This does still explain Ginny's infatuation - when her statement "I never really gave up on you" is taken into account - but once Harry's attraction to Ginny comes into play, he does not experience bonding moments for Ginny on such a scale again. Therefore, Harry has not yet even made the transition into infatuation for much of the love affair, let alone true love.
Point Two: Attachment, Trust And Unconditional Love
For mere infatuation to transform into true and unconditional love, the lover must experience a change in mindset. Throughout the phase of infatuation, a lover will say; "I love you because you are faithful/beautiful/funny/clever/charming." However, true love occurs when the "because" is dropped and the statement simply becomes; "I love you." During infatuation, a lover bases their love on the emotions that their partner makes them feel, but in true love, there are now no more conditions attached to the love, and the lover no longer appreciates the subject of their love for the emotions the subject makes the lover feel, but rather for the person the subject simply is.
This transformation is demonstrated beautifully in one of Ron Weasley's most vital scenes; A Horcrux has been tormenting him with illusions of Hermione and Harry locked in an embrace - echoing his greatest fear - and telling him he is worthless, that Hermione loves Harry more than she does him, and that Voldemort could offer Ron far more than Hermione ever could. Ron's response? Stab the Horcrux. Here, Ron's act of defiance symbolizes that no act of evil can damage his love for Hermione, and therefore that his love is no longer based around his own insecurities, but of his complete devoted trust of the person he knows Hermione to be. In short, Ron has moved from infatuation into true and unconditional love.
As well as proving his unconditional love for Hermione, this action represents a new stage in Ron's character; through resisting the temptations Voldemort has offered him, and combined with his sacrifice in returning to the Horcrux Hunt, Ron has confirmed that he is now emotionally ready for a relationship with Hermione.
However, at no stage throughout Harry and Ginny's romance do either lover commit an act based only on trust of their partner; at no stage do they prove their supposedly great and unconditional love for one another. Indeed, that Ginny's love for Harry is not based on trust is all but stated in Deathly Hallows, Chapter 29; where Harry's old flame Cho Chang offers to escort Harry to Ravenclaw Tower, but "Ginny said rather fiercely, "No, Luna will take Harry, won't you, Luna?" Here, the text blatantly implies that Ginny does not trust Cho around Harry. This Therefore proves that Ginny's love for Harry is not trustful and unconditional, for how can a lover completely love and trust her partner, yet still be jealous of said partner being in close proximity to an old flame he has not properly spoken to in two years?
Point Three: Sacrifice
Sacrifice is a great component of any romance arc, due to it being such a demonstration of a character's devotion towards their lover. Ron and Hermione exemplify a non-romantic love towards Harry when they sacrifice their seventh year at school to assist Harry in his hunt for the Horcruxes, once again solidifying the bond between the Trio. Ron demonstrates a sacrifice once again, when he returns to the Horcrux hunt after having despaired and run away is disgrace to Bill and Fleur. Here, Ron again establishes his love for Hermione, when, once having escaped a depressing, dangerous and most likely fatal Horcrux hunt, and despite being taken into Bill's safe home, Ron "wanted to come back the minute I'd Disapparated." Against all the odds, Ron rejoins Harry and Hermione, blundering through the forests with little hope of finding either of them, relying solely on a Deluminator gifted to him by Dumbledore, without any knowledge of how it works, and all along knowing he will face Hermione's wrath on his return.
He does all this anyway, and in the process confirms his great love for Hermione.
Sadly, Harry's sacrifice for Ginny does not carry the same weight. Harry and Ginny's great sacrifice was supposedly when Harry broke up with Ginny for her own safety, claiming that she was in danger as long as they were together. Whether or not this was true is irrelevant, because Harry does not essentially sacrifice anything. Harry spent much of Deathly Hallows on the run and as an outcast from wizarding society - it's not as if he would've had time to sneak in a couple of quick shags when hunting down the Horcruxes. How can Harry be sacrificing happiness and comfort with Ginny when he was never going to have the happiness and comfort with Ginny in the first place?
Point Four: Demonstration And Growth Of Character
A key aspect of romance writing is the impact a lover has on their partner. This is a reason I like the moment of Ron and Hermione's kiss so much; Ron has decided that they should evacuate the house-elves from the battle and that they cannot ask the elves to die for them. Here, Ron - previously disparaging towards Hermione's views on house-elves - has endorsed what Hermione has been saying for years; elves deserve human rights. Ron's new stance on house-elves represents to Hermione that she has had a positive effect on his personality and the better person he has become, and she acknowledges this growth with a kiss.
Yet this never occurs between Harry and Ginny. Not once does Ginny challenge Harry's personality, nor does his love for Ginny encourage Harry to become a better person. Again, fans might cite Harry and Ginny's conversation in Order Of The Phoenix; Harry worries he is being possessed by Voldemort and Ginny reprimands him, reminding him that she has been possessed, explains to him that he definitely is not, and tells him to snap out of it. Whilst this is an instance of Harry growing through Ginny's actions, Harry is not growing because of love for Ginny. Harry is growing because he is relived his not being possessed by Voldemort. Furthermore, at this point Harry is still entertaining feelings for Cho, and romantic feelings towards Ginny have not yet crossed his mind.
There are no other examples of Ginny causing Harry to grow as a person, nor vice-versa. Therefore, we can safely assume that they had little impact on their lover's character.
Point Five: Development Over Time
This is the most obvious point, and one of the major reasons the Harry/Ginny romance is so widely detracted. Whereas Ron and Hermione were friends throughout all seven books, and a romantic attraction was hinted at as early as Prisoner Of Azkaban, Harry's attraction to Ginny begins abruptly in Half-Blood Prince, with no previous hint towards this other than Ginny's childhood crush on Harry. Furthermore, there is little detailed interaction between Harry and Ginny from this point on; as well as their supposedly deep conversations taking place mostly off-page, they have no contact for nearly a year in Deathly Hallows. Ginny and Harry don't even get an emotional reunion at the end of Deathly Hallows - all in all, their page time takes up less than 10% of the entire series. This evidence further fuels speculation that the couple are still in the early stages of attraction; if Harry and Ginny spend so little time together, and are involved in about one or two serious situations together, then how are they going to bond and know each other well enough to create this supposed true and unconditional love story?
Point Six: Conflict
Lovers spark through their differences. Here, the old adage of "opposites attract" comes into play. The reason this is such a popular characterization device in romance literature is because of its usefulness in the aforementioned growth and demonstration of the romantic leads. A character's difference to their lover allows each lover's character to be challenged, forcing the lovers out of their comfort zone and testing their love. The key here is that the romantic leads must be superficially dissimilar, but have connecting souls; underneath the layers of their complex personalities, their hearts must be similar.
Ron and Hermione are a fantastic demonstration of this concept. Ron is her opposite on the surface; she is hard-working, he is lazy, she abides by rules, he ignores them. Henceforth, there is conflict between them; there is jealousy, arguing and anger, and all this makes them fundamentally interesting. It thus makes their long and complicated journey into lovers an emotionally involved and fascinating story. It's rewarding for a reader to see Hermione's kiss, because it means they've learned to co-exist and appreciate their differences - a genuinely heartwarming experience.
Ginny and Harry do not have the same dynamic. Due to Ginny's little importance in earlier books - apart from her Chamber Of Secrets role as a damsel-in-distress - she has a far less defined character. JK Rowling's comments do not exactly help, either; "they're both very strong and very passionate." At no point does Ginny force Harry out of his comfort zone, nor challenge who he is as a person. As a result, their romance is static and gives them little to talk about; indeed, this is implicit throughout their duration as a couple in Half-Blood Prince, where much of their activity as a couple is only mentioned off-handedly in this volume, suggesting that there is in fact much less to write upon the subject of their romance.
Conclusion; Despite Rowling and Harry/Ginny fans claiming about the lovers of this unrealistic pairing being "soulmates", they have a romance of true soulmates staring them right in the face; Ron/Hermione. Their outer personalities challenge each other's character and force the other to grow, yet their inner personalities connect; they are both loyal, loving and liberal people - they are the true soulmates.
Ron and Hermione are a fantastic love story, and it's a disservice to their romance to shove them aside and bang on about how beautiful Harry and Ginny's forbidden romance is - yadda yadda yadda. I genuinely wanted to like their romance, but their lack of conflict, sacrifice and growth through their love makes it an essentially weak and boring story.
Long story short; Ron/Hermione ---> Harry/Ginny