I think many people, in their quest to complain about the unrealistic skills Sokka showed with a sword after so little time, forget that he knows how to use a shit ton of weapons already.
Machetes, Clubs, Boomerangs, Sabres, Spears, and even Daggers. Sokka learned a lot of shit with these things, before he ever got a sword. Dude could slap darts out of the air with one swing of his machete. His aim with the boomerang is terrifying.
Sokka wasn’t some untrained pampered prince who’d never touched a weapon in his life prior to approaching Piandao.