It can also be argued that he's not.
Of what the ESPN site considers "qualified" centers, he is in the bottom 40% in: points, points/48, rebounds, rebounds/48, blocks per game, TOs, TOs/48, steals, and steals/48. He is dead last in points per shot, and second from last in FG%.
He is average in blocks/48, and above average in assists and assists/48.
His Roland Rating is around -3.3:
http://www.82games.com/0910/0910SAC.HTM
Maybe he does better using only offensive ratings? No, in PER he's 27th among centers:
http://www.nba.com/statistics/playe...itScope=GAME&qualified=N&yearsExp=-1&splitDD=
Add it all up, and I'd call him below average.
I do agree with the notion that a good C could make a big difference. I don't have much confidence in the vets we'd be likely to pick up as FA this year, but I see some possibilities in the draft. Not as many as I'd like, but... some.