<p>I think you have to take into account what happens when an Avatar gains control of the Avatar State. Guru Pathik says that when Aang opens his last chakra, he will be able to go in and out of the AS at will; and within the Avatar State, Aang will have complete control of all his actions. So, in a controlled AS, Aang would need to primarily rely on his own skills because the past lives aren't in control, like in a defensive AS. Korra would do the same because she is in control. </p><p>Roku says that the Avatar State empowers Aang with the skills and knowledge of all his past Avatars. This does not neccesarily say that the past lives power the AS- it says that allowing Aang access to his past lives is one out of the possible many abilities of the AS. Roku also prefaces this with saying that the AS is a defense mechanism, which is one feature of the AS and not the only use of the AS. </p><p>ATLA showcases many abilities of the Avatar State, but never really touches upon the essentials needed to make it work. TLOK shows what the Avatar State is at its base: Raava and Wan combining their energies resulting in an increase of power for both of them. So I don't think the AS was retconned- just that the inner workings of the AS hadn't been revealed, yet. </p>