12. Dwight Powell
Every season that Dwight Powell has been in Dallas, he's exhibited that he is the ultimate professional and this season has been no different. Powell has fought against initial expectations of not being in Dallas' rotation, as he's been Dallas' main backup big-man this season.
Despite playing his least amount minutes since the 2015-16 season at only 16 minutes per game, Powell is playing his role to an absolute tee and is doing everything in his power to contribute to winning basketball for Dallas. Powell gives great effort every possession when he is in the game and brings a great veteran presence in the locker room for Dallas, so Dallas couldn't ask for a better teammate to fill the backup center role.
However, the Mavericks could certainly ask for a better player at backup center, as Powell's deficiencies from a defensive and rebounding perspective have been well documented throughout his career. Powell isn't a poor backup center by any means and he's especially valuable for Dallas due to his advanced understanding of Dallas' system, but it's hard to play him elongated stretches when his rim protection is as poor as it is.
Powell's athleticism seems to have depreciated a little bit as he's been far less dynamic offensively this year as well, but that's to be expected as he'll turn 33-years-old this upcoming summer. Powell gets a C+ at this midseason mark since he's fallen off some this season, but has still fulfilled expectations at the same time.