This had actually been discussed in another thread viewtopic.php?f=39&t=47367
, but it got ignored possibly due to the subject title not stating the problem outright. Yet that thread reveals a serious flaw in Possessor, that is, Possessor cannot use any weapon-specific talent when the Possessor himself is not equipped with the required weapon. That means you cannot use any archer, brawler, and shield-wielding class talents of the assumed forms, and you can only use assumed forms' 2H and dual wield talents when you are so equipped.
This makes sense for other classes. But when the essence of Possessor is being able to use enemies' talents, denying Possessor any benefit to possess, say, an archer rare, would greatly limit the fun of playing a Possessor. Of course Possessor is perfectly viable by just possessing Demon/Dragons/etc., but I don't see the point of limiting the choices.
Let me rehash my old suggestion here: There could be a default mechanism which allows possessing to also copy enemy's weapon, and such weapon will only be used for using the talent of the assumed forms. The relevant weapon mastery level will be determined according to the min of 1. Enemies' weapon mastery 2. TL of Full Control