One of the things that I think is hard to value at times is mental toughness, the toughness that brings swagger. Lowry spoke of it the other night (after the loss to the Celtics), and he lumped swagger with a physicality or perhaps the word I am looking for is edge. I don't believe that Jaylen or Jason (or Walker or Hayward for that matter) currently possess that edge that the playoffs require. With the Js perhaps it is youth, perhaps it is just a function of who they are as people, who knows. I believe the team was missing that aspect when they got pushed out of the playoff bubble, lacking a bit of an ability to push back to some of the physicality they were encountering. They missed some of that Baynes sandpaper, that Morris edge. It rubs off on teammates, it is contagious at times. They have it in Marcus, but I think it helps to have it in a big. Someone who can and will set a hard screen after a teammate was fouled a bit too hard. Someone who can make the defender hesitate going over a screen.
I believe that the TT brings some of this to the table, and that part of what he brings is as valuable as the Xs and Os. Team building is sometimes more than just physical skills, and having the right complementary players is a complicated. Sometimes it's the player with the physical ability to hit the open 3, sometimes it finding the player like Teague who will defer to the young guns, sometimes it is less about a physical trait and more about the mentality they bring. Some young teams need a veteran to teach them a work ethic - how professionals carry themselves (I don't think any of the current C's need that). This Celtics team (those that remain after the bubble team) need that sandpaper, that pushback when the refs are allowing teams like the Raptors or the Heat to get a bit physical (and they do and they were).
I'm NOT predicting that TT is a good fit, or that he will be successful at his role, only pointing out that I believe that Ainge was looking for more than what we see in the box score, or metrics that talented people like Bowiac develop. "A team that is more than the sum of it's parts" kind of thing.