Oh yeah, there's a big difference when it's supposed to be true love. If you're presenting something as true love you have raised the bar for yourself--you have to make people believe it. Or else just accept that it's flat--like having Arwen show up at the end of LOTR. In that case we don't really doubt it because we're just told it, but it's not like you have any clue just what they see in each other besides that they're who they are. Sam Gamgee is in an even odder place since Tolkien unfortunately seemed to want to end him with a happy marriage that implied his personal love for Rosie was important while completely spatchcocking her on in the end. We can accept "and then he went home and got married," but if it's supposed to be important who he married, we won't care if we don't know her.

But yeah, that's the thing in HP. It's not that I have any trouble believing that Harry wanted to date Ginny, but as with everyone else in the books we're being shown petty teen romance that we're then supposed to take as something that lasts a lifetime and that's a hard one. If the books had gone from GoF to the epilogue you could swap Cho in for Ginny and get exactly the same result because all it's really saying is that the girl Ginny likes now is his wife later.

Re:Avatar that is totally what the person was referring to, I think. The comic book was brought up as explaining how Zuko and Mai got together and the person said why should we accept that happening somewhere else and not Zutara? Which just struck me as odd because Zuko and Mai didn't happen off-screen. I, personally, didn't need to see them go from two kids who knew each other to two kids who were dating because I figured there wasn't really a story to it beyond that we know she liked Zuko so Zuko then went out with her. It wasn't true love at that point, it was just a goofy teenaged couple. Once they're going out Mai acts as a confident and counselor and Zuko talks to her. They really didn't know each other well when they started going out imo.