This is going to be a tough one. I think OKC has an edge with Rose and Howard over Nash and Big Al (even if Roy's stats say otherwise).
And aren't those stats important to consider?
I focused on the last five games so that folks couldn't say I cherry-picked, or was relying on games from many years ago that don't matter. However, for their careers, Big Al has held D12 to 15.9 points, so it isn't a fluke.
Big Al vs. Howard is neutral.
If you ignore their defense (and rebounding).
Big Al is a major liability on team defense and Dwight Howard is one of the best help + interior defenders in the league ... if not the very best once again next season.
Big Al can score with D-Howard -- heck Big Al is better offensively with his abundance of post moves and superior jump-shooting -- but he cannot match what Dwight Howard gives his team on the other end of the floor (or on the boards).
But isn't most of the defense head-to-head?
I would say (guess!) as a general guideline, in the league today (different from other eras), that defensive responsibility for a center (as opposed to other positions) is about 70% team defense and only 30% man-to-man defensive sequences.
The difference between center and other positions being the role of defensive anchor (basket protector) and also the lower number of offensive talent at the center position relative to other positions.
If you look or think about the number of plays someone like Kevin Garnett is asked to make as a defensive anchor for Boston showing on help defense coverages vs the number of times he is asked to do something one-on-one defensively with his own check ... the number of help defense sequences far outweighs the number of one-on-one sequences. 70-30 or something like that is just a guess at the difference.
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Although, that is not quite true in this specific matchup.
One of the reasons for such a large difference in team defense + man defense situations is the low number of centers who are high level offensive threats. In this case, Big Al and D-Howard, they are both 20ppg threats. Two of the best scoring centers in the league. So man-to-man defensive responsibilities a lot higher and closer to 50-50 team D vs man D.