Pierce was probably a little better in some regards, but he played on a lesser team without a go to guy like Kyrie, which Jayson had much of the year. JT's #s were a lower because he spent a good deal of the season standing on the 3pt line while Kyrie ran the offense with Horford.
But if you handicap it because PP was 1.5 years older as a rookie and had 3 years of college ball under his belt, then Tatum's was more impressive. Exciting that we can have this conversation with a rookie compared to a lock HOFer who was one of the best players of his generation.