You make an interesting point about Sokka/Toph that hadn't occurred to me until now, but I definitely see the sense of it. Sokka does have a bit of a sore spot about the bending thing, and you're almost certainly right in that it would have to come up at some point between them. Sokka and Suki meet on unequal terms, too, but her greatness is attainable, and Sokka loves a challenge. He's capable of becoming a great warrior; he will never be able to make rocks spontaneously fuse or fly, and Sokka hates dead ends.

(Incidentally, as for mutated character dynamics in fanon Zutara...I'm a Katara/Zuko shipper who developed independently outside the fandom, then poked my nose in to see what the fanon take on them was and felt like the kid at the beach who curiously pries up the pretty rock and suddenly has swarms of fleeing sand lice skittering all over her bare feet. Those two have a great dynamic, both present and potential-future, just the way they are in canon. If only more than 5% of their fanwork would actually pay any attention to it...)