No, he really was that good. If you take out a few games where like Arizona and Seattle go all in on stopping Stacy because they didn't have to worry about Clemens, his average goes way up.
Next year, with Sam in the game and Robinson blocking for him, he should be very effective.
In the Carolina game, for example, their defense DID key in on Stacy and do everything to stop him, and he was still churning out a few yards in 8-10 man boxes, and if you noticed that was Sam's best game, the passing offense was really clicking, it looked top 10, we just made too many mistakes like dropped passes, INTs, and tripping penalties. So if teams do everything to stop Stacy, there are consequences.