Davis even plays the 3 because Monty looks for any and every reason to have him on the floor at all times because the unibrow's defense is godlike.
Noel can play the anchor role just fine (mainly because he's mobile and knows how to be mobile)... I don't think people realize exactly how much of a complete 180 Drummond has done since he's been drafted and are using that as a way to understate a bunch of other factors that go into transitioning to the league.
Yeah Noel is an even better defender than Davis was in college. He has at least a block per game wiped off the boards by stupid fouls by the primary defender, otherwise he would be on pace to break Davis's mark for BPG by a substantial margin. That's not even mentioning his steal rate.
The one thing he doesn't do that Davis did is close out on jumpshooters for blocks, but that's just because if he did that, Kentucky would never get another defensive rebound.
Other than that he is better in every respect on defense.
On offense he is way worse, but his post-up footwork and moves are ahead of where Davis was at this point last year. He has no jumpshot and worse FT shooting than Shaq though, and he clearly doesn't have the bulk to be a consistent post up player yet, so his offense is going to be limited.
I don't know if you draft a one dimensional player #1 and I don't know how much a defensive specialist would help a team bad enough to get the number 1 pick, but defensive big men on that level don't come around that often at all.