The Mavs center position is far from a strength on the roster, but it is nice to see that there are multiple guys that can play that role for the team. Bringing Nerlens Noel back is nice, despite the means by which it happened, and adding Jeff Withey gives us a little bit of depth. Add in the fact that Dirk, Dwight Powell, and Salah Mejri are all back and there is no lack of big bodies.
Dirk is a traditional 4 but has been playing a lot of center in his later years. Although he struggles defending opposing centers, he struggles a lot more with opposing power forwards.