I think at this point the Celtics are who they are and you gotta ride with it.
Marcus is who he is. He could play the way you want, but he might jack a bunch of threes, hit them and win a game.
Jaylen is who he is. He is going to isolate and try to dominate his man advantage and it could lead to a couple ugly turnovers. He could try to change, but that could lead to him not having a 4th quarter like in game 1 where he used his dribble to then dominate and push the team to victory
Regarding the jump shots, yeah, I would love more runs at the basket, but the two best guys at this create lots of turnovers when they do it and you already complained about Jaylen doing it. Best thing is to take what the defense gives you while running your regular offense as aggressively as possible. If that means hitting open jump shots, you take them. If it means going inside you do so. They're not going to change that approach, they've been doing it all year
Boston has shown all year that the guys that are open from three are going to take those shots. So whether it Tatum, Brown , Al, Pritchard, Grant, Smart, White or Theis, the guy open on the three, if it's wide open, is going to take it. That's who the Celtics are, that's not going to change by trying to funnel the ball to and away from certain three point shooters.
Theis got some court time already. He might see more. He might not. That depends on a lot of factors with the biggest being health. If Rob Williams is healthy enough to play lots of impactful minutes, he should play and Theis should sit because Rob is the more impactful, better and more important player. If Rob is limited and not that effective unless played in much less minutes, play Theis. Kinda been that way since Theis got here and, once again, that's not going to change.
At some point everyone needs to embrace these Celtics for what they are and live with the little things that might drive them crazy. They are who they are and who they are has been the best team in the Association for the past 55-60 games that's just 3 wins from a title against a very beatable team. I for one think, just the way they are and the way they play will be good enough to raise banner #18.
So I hope they stay the way they are, just stay aggressive, play Smart and everything will work out from there.
Then in the off-season, get better at some stuff and enact some change and come back better to defend that title.