If you go to a random pickup game in the local gym, you'll see plenty of 6-foot centers. Coincidentally, most of the 6-foot centers in BB are not much better than your average pickup player.
The way the game is set up, you'll rarely see a 6-foot guy among the top centers in the game (or a 7-foot guard, for that matter). Also, height by itself has no implications on in-game performance.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."