I think Tony Bradley might be okay as a backup center, if he doesn't have Georges Niang playing next to him. Bradley's main responsibility is to rebound and roll to the rim on offense, and he does those things pretty well. The issue I have is that Niang is soft defensively and is a mediocre rebounder. If we had a beast at the 4 playing defense and rebounding, I don't think people would have a problem with Bradley so much.
Obviously, Bradley isn't the rim protector that Gobert is. Nobody is. It's going to be difficult to upgrade the backup 5 spot, however. We're on a tight budget, and other than, say, Jakob Poeltl, I'm not sure who really does it for us.