The fact that TO is our most effective big man says more about Nolan than it does about TO.
We all knew Brimah would be raw, that we'd have to live through the growing pains as he figures out proper defensive positioning, rotations, and rebounding technique, not to mention everything about the offensive side of the ball.
Nolan, frankly, has been a disappointment. He looks exactly like you would expect from a kid who we picked up late because we had no other options. His instincts are poor, he's not a good athlete, and he comports himself tentatively, as if he knows he has no business on a high-major basketball court. I was hoping for something like early-career Hilton Armstrong out of him, and he hasn't even given us that.
Olander, despite his glaring physical limitations (quickness, strength, jumping ability), has a good set of instincts, knows how to screen well, generally is in the right position, even if he doesn't end up with the block or rebound, and can actually give us something in the half-court on offense with the ball in his hands.
At this point I'd split the minutes primarily between TO and Brimah, with an eye towards grooming Brimah to be our starting C next year. Nolan will strictly be a 4-year backup. I haven't even mentioned Facey, whose role is particularly murky (not helped by the fact that he hasn't gotten any minutes); he has the physique of a 3/4, but only has the skills of a 5. I'm not sure where he plays in the Ollie system.