I know their box score stats are pretty comparable, and it's easy to look at them side by side and say they're within throwing distance of each other, but Tatum's net rating was +2 and Jaylen's net rating was -1
It's possible this is a function of who they were paired with, but Tatum on the floor meant the Celtics were separating from their opponents in a positive way, and Brown on the floor meant the Celtics were losing ground.
I don't look at this metric all on its own, but I think the fact that Tatum has led the team in net rating for a few seasons now IIRC is a big indication of his impact on the floor and can't just be ignored.