Probably. He might even be better than they were...but the tough truth here is that P has to help this team win Championships to be widely acclaimed as an all-time Celtic great. It's not totally fair because Championships are about the team, not just the individual, but that's the standard when you're looking up at 16 banners.
i started watching ball the year they drafted reggie lewis, and he'll always be one of my all-time favorite players, but pierce has definitely surpassed him. having only seen bill sharman and sam jones on film, i still feel pretty confident saying that if you wanted to build a team you'd be better off with pierce than either of those hall of famers (talent over accomplishments in this case). i guess it depends on how you want to rank your celts. sharman and sam were both very prolific scorers on the greatest dynasty ever, so there's no comparing truth to that sort of acclaim, but he is probably the most unguardable 2 the celts have ever had. i think if you built an all-time celts team with your goal being to beat any team in any era you'd have to take pierce over either of those guys (though havlicek might get the start in front of him). i think my team would look like this:
w/ kc, sam, jo jo, reggie, and walton as our ir guys. so in answer to your question, it's a contextual thing, but i do rank pierce ahead of sharman and jones etc. but not havlicek. and damn do i miss watching reggie lewis can that baseline pull-up in everybody's face!