i think that the reason aang isnt avery powerfull airbender (or seems that way) is because
A. he isnt a real airbending master yet, hes only had 12 yrs of preactice which isnt that much compare to Bumi who has had 112 yrs or the other masters we have seen i.e master??Pako and master Jon Jon,??which i think might mean he gets taught by and older airbender possibly from the western air temple(who by air bender rules are only female)
B. because he is afraid of inducing the Avatar state and hurting is friends like in the first episode of the 2nd book- Avatar State. we saw how he felt in The Deserter when he burt Katara's hand he swore he would never firebend again.
please get back to me on this and plus if there are any hardcore fans who get the lastest film on there pc's and want to send them to me email me please!!!!
also someone put Bitter Work preview on Youtube!!!