Advance skills

although there arn't that many memebers in here, a future problem i am conserned with is the advance skills various bending arts may have.
some problems i see in the problem are
noob fire benders learning how to lightning bend or how to redirect it
noob water benders learning how to heal like katara
noob earth benders learning how to bend metal
the only bending art that has yet to show any advance form is air bending

the reason why i find it a problem is that if we dont' follow those rules. then it would be inconsistent with the story as there has only been one recorded earth bender that knows how to metal bend. and that not even the avatar has learned how to metal bend before, even after the discovery of metal. fire bending lightning is often something only teachers could do, i'm not saying that noob fire benders can't redirect lightning it self. but they can't just say they already learned it from some one else. as for the healing part. sure katara said she always knew, but she has yet to realice it till they met jong jong.