Just checked his draft weight... 6'7' 250 pounds. Though he really didnt start declining until age 32. All the years from 2001-2012 were pretty outstanding, even as he gained weight. At that point he was listed at 300 and then had the knee surgery in 2013. But didn't even truly suck until after that.
So, while he didnt get worse while gaining the weight, there's probably some sound logic to the fact that had he not been so heavy, his knee would have held up better, maybe not requiring surgery. Also, depsite losing a bunch of weight after the surgery to try and aid in recovery and put less pressure on that knee, he was still just a really big dude. So he didnt really get worse from the weight gain, until his knee gave out.