I don't just consider the bending element, I also consider what nationality the character has.
Yes, Korra is the Avatar and therefore can bend all four elements, but she's water tribe.
Asami is a nonbender and is considerably both Earth Kingdom and Fire Nation, so Korrasami would kind of be considered opposite elementals.
But on a personal note, I want to considered them to just be besties who take on some action and help each other with girl stuff like one day helping pick out wedding dresses rather than a romantic ship. The fandom just turned it into an annoying mess that makes hiss and scratch at my computer screen.
But if you ship it, that's okay.