Jayson Tatum 2020-21 4th NBA Season 2X All-Star 25.7 PPG 7.1 RPG 4.2 AST (Age 23)
Paul Pierce 2002-03 5th NBA Season 2X All Star 25.9 PPG 7.3 RPG 4.4 AST (Age 25)
I think your age is a little off. At the start of the 2002 season, Pierce was 25 but 26 at the end (Born October 1977). Tatum was 22 at the start of the 2020 season and turned 23 in March 2021. You don't have apples to apples. You either have to say they were 22/25 at the start of the season or 23/26 at the end.
Doesn't take away from the point though, perhaps even reinforces it. Tatum is doing well as compared to Pierce and doing it at a younger age.
Pierce could draw more fouls and even if the numbers don't show it, Pierce was a better rebounder as he could muscle his way to getting some really important rebounds. Tatum is a better pure shooter but not as versatile of an overall scorer (at least not yet).