Im not in love with the defensive scheme (particularly the ball screens) but I'm not sure there is a player left who is an unwilling defender.

The only question marks would be:
Darius Maddox
David N'Guessan
Cordell Pemsl (to a degree)

I suspect Maddox will be an average defender, and N'Guessan will be average to above average. Pemsl will depend on how quickly he can shed a former defensive system to play in a spot where the changes are the greatest. I dont think he will be an unwilling defender, but he could take some time to keep from reverting to old tendencies