The killer for Bradley, as this thread indicates, is the ambiguity. Three years in, and we do not have definitive answers to some very basic questions:
Can he consistently guard SGs?
Can he consistently guard bigger PGs?
What position should he play most often?
Can he ever become an adequate enough ball-handler to play PG, even in spurts?
Can he be a starter at either position?
Will he ever be an average or better 3 point shooter?
Can he develop a jumper, or some other offensive weapon?
Right now we know that he can create absolute havoc as an on-the-ball defender of opposing PGs. That seems, to me, undisputable.
But the unknowns, about critical aspects of his game, far outweigh the knowns. The injury plays a role, but I think that can be overstated - he's missed half a season out of 3.
One other comment, about trade value specifically: AB's probably varies tremendously from team to team. I think CLE or GSW would jump for joy to have him, because he can play alongside Irving/Curry, who have enough offensive firepower all on their own, and AB frees them up by defending the best backcourt scorer at either position, because those guys are also bigger and can defend many SGs.