This is my take as well, though I would add that I question whether he's athletic enough to ever be a 'superstar'. His ceiling may simply be solid NBA starter but he's taking this approach that he has to be 'the guy' when he's got possibly 3 better players on the court with him plus a 5 in Kanter who has proven that he can score consistently.
There are not three more talented scorers on this team than Jayson Tatum.
Kemba is a better scorer now, Tatum has a higher ceiling.
For the Celts to get to where they want to go, Tatum has to become a lead scoring option. He's demonstrated that he has the body, the skills, and the stamina to do it against good teams. He's got work to do, but if he is just a solid starter, the Celts are going to be stuck in mediocrity for a while.
Nights like last night are just part of what the Celts will have to go through if they're going to have Tatum work his way into the kind of player they need him to be.
He may never get there, but if that's the case, it's good to know.