In the NBA he's going to have to do more than just defend his guy, he's going to have to learn team D and play the pick and roll, 2 areas where he often out position and lacking in understanding on how to defend him. Also there's a big difference in the NBA when you just can't park yourself in the lane and defend the rim. One of the big reasons why Hasheem can't stay on the floor even for D is because he doesn't know where he's supposed to be and can't defend the pick and roll. I'm not saying just because Hasheem struggled Andre will but there's a much bigger adjustment to playing D in the NBA then in college when you have more responsibility for the overall team D.
Hasheem was/is not physically capable of defending the P&R. It wasn't just that he couldn't learn it. Hasheem is slow laterally. I dare you to describe Drummond as slow laterally. Drummond will have to learn how to play P&R defense, but he has the physical ability that Hasheem just doesn't have.
Drummond rarely (if ever) played a one man zone like Hasheem did (which was great for UConn but not good for the NBA). Drummond was usually defending 4's, because Alex was unable to defend outside the paint.
Davis actually does have some back to the basket moves. If you watched him in the tourney you would have seen a number of lefty and righty jump hooks and turn arounds. He also shoots about 50% points better from the line. And he has more of an excuse for his developing post game than Andre because he hasn't even been a big man for 3 years.
You may be right that Drummond has a higher ceiling but not much higher and Davis is much more likely to reach his ceiling.
Yes, Davis has some back to the basket moves. It's actually odd. Watching Davis, I would have never guessed he was once a guard. His jump shot is passable for a big man, but pretty horrid for a guard.
I'm not sold on Davis being a great superstar player, but I think he has multiple all-star appearance as his ceiling. Drummond's ceiling is probably similar. Both will have issues. Davis' thin frame will be OK at the 4, but will struggle at the 5. I do think Davis is more likely to succeed, but a lot will depend on where Drummond goes.
I think Drummond can excel at the P&R offense, with the right PG, right away. Drummond was better than Davis on the offensive boards, though Davis was much better on the defensive boards. I thought that was interesting.