I compare it to the Dumbledore situation because Korassami is technically canon in that same way that Dumbledore is technically gay.
Yes, they held hands; but to a lot of people this doesn't really mean a lot. Yes, you could very well look at some of their recent interactions as build-up to a budding romance; you could also look at these as just genuine moments of friendship. Solely within the context of the show, it IS ambiguous. Certainly less ambiguous than Princess Bubblegum and Marceline, but ambiguous all the same.
Bryke supposedly confirmed it. Okay, but this is where the Dumbledore comparison comes in because the fact that it needed to be confirmed at all by the creator AFTER the fact (and not in-story) says a lot right there. Not everyone follows what the creators say about their works.
Bottom line is that it just feels half-assed. If they are a couple, go all the way. They don't have to fuck on the spot, but maybe have one of them say, "I love you," or have them kiss or whatever. Make it more concrete than "look at the parallels between them and other couples holding hands!" To be fair though, it IS possible that maybe the writers just weren't allowed to do more than that even if they wanted to, so it had to be censored down to just hand-holding.
Keep in mind, I'm not disputing whether or not it's canon. I don't really care. I hated the stupid love triangle business in the first 2 seasons that it completely turned me off any of Korra's romance (I actually would have preferred her staying platonic with at least her group of friends, but whatever). I'm also not a shipper, so I personally didn't care about Korra and Asami getting together; I also didn't really care about Aang/Katara, Jinora/Kai, or Sokka/Suki (though I did think Bolin/Opal was kind of cute though and Zuko/Mai was fairly amusing).
What amuses me is how so many people are now praising Korra as opening doors for same-sex couples in kids' cartoons when Clarence actually did it first by having two legitimate same-sex couples- one lesbian couple even being the parents of the one of the main characters.