Bogut is a non scorer, no matter what team he plays for. He is a D guy. Period. The kind of player they need, though he isn't very durable.
The Celtics are thin in depth, and need all their starters to be competitive with the better teams. That hasn't happened much so far this season. You figure IT is going to miss games, after playing 82? last season. He is a high injury risk going to the basket frequently.
Aside from that, I don't think they can get to the next level with the rebounding and rim defense they have. You can't win on the perimeter, unless you have a bunch of sharpshooters out there.