the reason aang seems to be "weak" is because his emotions are holding him back, when he finally releases this emotion (i.e. letting go of katara) he got blindsided with a lightning bolt. Azula knew he was up to something so she did it which makes her a genius and not like other nemesis in which they wait for it to come to them. I do think that toph is very powerful now, probably at the level of king bumi, considering he thinks "out of the box" he will figure something out how to defeat toph which is pretty actually...
round 1 fight!
king bumi turns the whole field into sand...game over
That's her weakness, its a major weakness actually and im pretty sure she will not overcome it because if she did, she'll be uber powerful and the writers dont want that.