Na. Perhaps that would be true if all we saw of their relationship was Book 3, maybe, but Book 4 was riddled with bigger hints that many people simply couldn't believe meant Korrasami because "it's a kid's show" or "they wouldn't do that." But those hints were there, from Korra saying "I don't know why I can talk to you about it and not the others" and her blush, etc.
And look, people were willing to accept Mako suddenly falling for Asami as some normal heater crush, and also were accepting of Bolin's flings with psycho girls, quirky and cartoony, but "normal" for a heater character.
But apparently Korra falling for Asami and viceversa needs to be EXTRA clear. Yeah, it could have been better written, when it comes to they hanging out with each other more, although that was a problem with Asami's character in general (why is she friends with any of them in Book 1 and 2?), but honestly, why can't it be just as spontaneous as Mako and Bolin falling for girls? Or Opal falling for Bolin, and Jinora falling for Kai?
That isn't to say it came out of nowhere, they were indeed building that relationship since Book 3, but what Bryan is trying to say is "you give hetero characters the chance to simply fall for other characters, try to do that with Korrasami, at least."
I'm a gay man, and even I had a hard time believing Korrasami was possible or to be taken seriously. Why? These last couple of days I realized that it was because I did indeed see their relationship through "male homo" glasses, paraphrasing Bryan.
I had no problem seeing Bolin as possibly bisexual when he thought Desna was a girl and cute, and immediately saw one of the Beifong twins as gay (wing or wei) after he was caught by Bolin and gave him a lovingly look because I'm much more familiarized with male homosexuality and trying to look for it in media than lesbian relationships, so yeah, I can accept that I missed the cues but on a second look, they're definitely there.