If this is the kind of return you are going to get for Walker, it is exactly the reason you can't move him (now or ever). Even if he is considered overpaid, Walker is just too good to trade away for much lesser pieces. As a win-now team, we are supposed to be the team giving up lower level players in order to acquire a guy like Kemba, not the other way around.
If you think you can get a comparable player to him that you think might fit better, like Vucevic or Collins, then by all means make the argument; but this just makes the Cs worse while also giving up picks in the process.