Yeah well, in that case Jeong Jeong can use blue fire, shoot lighting and use combustion. He's just never shows it.(that was sarcastic) I'm pretty sure Iroh can't use blue fire, cause if he could he would teach Zuko.
And Bumi isn't blind so he doesn't have that disatvantage. And you may be right about the tower, but we didn't see Toph bend a statue of 300 tons. Or a whole city. And being able to bend metal doesn't mean you are better at bending earth. I know some fighting skills that a friend of mine (who is nearly a black belt in Karate) doesn't know. But still I can't defeat him in a fight. But the skills I know are lethal, an more powerfull. But it doesn't mean I'm better at Karate of fighting at all.
And yes Pakku did hold back. He even said "I'm not going to hurt you". And I just watched the fight, and Katara didn't do that wel. Pakku easily blocked all her attacks and put up some good ones against Katara. She actually was helpless.
So, you get my point now? Being able to do stuff (bend stuff) another fighter (bender) can't do, doesn't mean you are a more powerfull or more skilled figther or better at Karate (or a better bender).