I think its close and we are watching Tatum pass Pierce in real time.
Thru 4 seasons Pierce had 1 All-stars, 1 All-NBA (3rd Team) and MVP votes in 2 seasons (highest 11th)
Thru 4 seasons Tatum had 2 All-stars, 1 All NBA (3rd Team) and MVP votes in 1 season (12th)
In year 5 Pierce was All-Star, All-NBA (3rd) Team, MVP votes (11th)
Tatum is All-Star and expected to do better than 3rd team ALL-NBA and better than 11th in MVP Voting.
Tatum seems to be more efficient, but if you look at the league adjusted numbers it's not as clear. Pierce performed better relative to his pears in stats like TS%, even though the raw number is lower than Tatum's.
Tatum has certainly had more playoff success to this point, but he has had a far superior cast. If Brown = Antione, what about Kyrie, Horford, Hayward, even Kemba?
I think Pierce reached his peak around year 5 and maintained it for about a decade.
I don't think Tatum has reached his peak yet, and if he does in a year or two he should be able to maintain that high peak for a similar amount of time.
So I's say Tatum = PP
If it isn't Tatum > PP as soon as this years playoffs I'll be disappointed.