Yeah, I guess Aang would have already known about energybending before the fight with Ozai even begins, right? Since of course he has his encounter with the Lion Turtle before it starts.
But, wait, if he already had that info, and that ability, why doesn't he try to do it from the start? The whole reason it feels like an asspull is that it's not handled logically. If Aang, BEFORE the fight, knew how to energybend, why wasn't that his goal from the beginning? What's the point of fighting Ozai the way he does at all? Just try your hardest to pin him to a wall or cliff with earthbending, and then use the energybending. Fuck, this actually makes me hate energybending MORE, since if Aang already knew how to do it before the fight started he didn't actually CONDUCT the fight in a way that makes sense.