On a team that is noted for not playing together and not moving the ball well, Jaylen can literally go several games in a row without an assist. His assist to turnover ratio is poor. His free throw shooting is also below average.
His 3 point shooting has been a positive, and in todays NBA that's certainly a plus. Where Brown really excels is in the open court in an up-pace game, exactly where the Celtics seldom play.
OK, but look at the title of this post. Jaylen has always been asked by the team to play a certain way. We know he would like to handle the ball more because he has said so, while to his credit, he has consistently done what was asked.
He just doesn't act as a primary ball handler very often. Tatum, Walker, Smart, Al when he's been here, Fournier, whatever backup point is in, all handle the ball more. When he gets it, he does something immediately, or moves the ball.
I think he could transition to a larger ball handling role in a few months if he had to, because he is amazingly adaptable. But he has always fit into much tighter constraints, while Tatum has been allowed to work out running the offense from day one. As he has scored more, he has expanded his ball handling a bit, but the only player I can think of who is better at scoring with less of a need to pound the rock is Klay Thompson.
Walker didn't adapt much. Smart doesn't adapt much. Tatum has a full green light. I would say the answer to this post is that Jaylen has always been willing to adapt to what the team asks of him, more than anyone else.