I felt it came out of nowhere, and I'm in the camp that supported the concept of Korrasami and wanted it to happen. Especially in the finale - there was literally zero signs of it until near the end, which I absolutely hated.

When you compare Korrasami to other ships, it's just not as direct. With Kainora you have other characters directly mentioning Jinora's "boyfriend". With Zhurrick you had Zhu Li lying on top of Varrick, and then the repeated comedic buildup of Zhu Li expecting Varrick to reciprocate her feelings. The setup is extremely transparent. But with Korrasami the signs were all objectively more subtle, even if by quantity there were (many) more of them.

Ironically, it's gotten to a point where audience itself sabotages the "show, not tell" maxim and allows writers to get away with it. There's literally no buildup at all to Kainora or Zhurrick - the audience is just given immediate and obvious cues that there is an attraction and they accept it (they're both attractive, young, eligible, etc. so why not?).

On the other hand, Korrasami was gradually incorporated over a couple seasons - and yet for many (such as my friends who were never exposed to the concept of Korrasami Inception-style), none of the moments were obvious enough to seem like a natural progression of the plot (let alone be the capstone to the entire series).

Could that be reflective of the difficulty that shows have in portraying same-sex relationships? They often need to break through a veil of uncertainty before being accepted by the viewer. Because it's not obvious for the vast majority of the audience, for better or for worse.

I believe that the execution could have been improved with more support without toeing the unspoken line of controversy (though I also just wanted to see more canon Korrasami). But as Korrasami was instead developed in with a more delicate and indirect manner compared to other relationships in ATLA/LoK, it seemed sudden and abrupt.