Hobbs nailed exactly what I was going to say in the very first response.
If any Celtics player has ever been massively underrated, it's Havlicek. Havlicek is seriously one of the best players of all time that nobody talks about, and the fact that this thread was made just illustrates the point.
Bill Simmons actually makes a good point in his "book of basketball" that Havlicek has gotten the short end of the stick in history partly because he was a white guy dominating when the league had more white players. Had he been black, people would have looked back and thought he was a revolutionary, Lebron James-esque player. No way to know if Simmons is right about this but at least it's an interesting theory.
At any rate, Pierce is my favorite player of all time, but it'd be hard to call him better than Hondo.