Really? Up until Korra, I always thought it was handled pretty well. The only kids show I can think of that did it better I Steven Universe
I think the biggest problem with Korrasami was just how totally out of left field it was. I know, realistically, that's how love is sometimes (Mai and Zuko being the perfect example. Although I actually love that ship) but in something like film and television, the audience usually likes to see some build up to the romance. Instead we get a few scenes showing that they've become besties in between seasons 3 and 4, and Bryke thought that was good enough to warrant dedicating the final scene of the show to those two. As if this was anything like the big Kataang finale people had been waiting for for three seasons.
I guess. Its been months since I watched LoK so I don't recall a lot of it but they seemed to be getting a lot closer starting book 4 so I don't think it was really that left field. Then again a lot of people thought Naruto and Hinata was left field so there's that.