I watched some games of this series, and what I saw a first problem is that MIL coaching needed to be better. BOS was more playing like a team, far more than MIL.
Now, it's certainly due to Middleton being out, but I think they could do a better adjustment
The one thing that is important is to have your full roster healthy, from the beginning of the season, more than anything.
If everybody stay healthy, you have great chances to advance further during the playoffs.
I agree that we need to improve the roster, but I fully disagree on doing that based on a 1-4 first round exit and like this team was fully healthy.
Now, we don't need to get all spot dominating as, among the four teams remaining, only BOS is this case this season, and MIL last season when winning a title had mainly the PF spot dominating (+9) and the other neutral (what DAL has this season with PG at +9 and the other neutral or negative).
Between two years ago and last year, we have improved SG, SF and C spots.
Between one year ago and now, PG got even better, SG and PF didn't changed, C a bit less dominant, bur SF decreased.
2019-20

2020-21

2021-22

But as we got torched by opponent wings in a lot of lost games, it's where I would target improvement, and why a guy like Simmons (if not shooting 3s doesn't create problem for the other guys) would make more sense than injury prone AD, or some of shooting guards that don't play defense like Mitchell, Beal,... and I don't want to trade Bogi as he was already good last season, but this season, it was simply with him that the team was playing best.
I would move Huerter and Collins before him.
Regarding Hunter, I would keep him, but if he can't bring the same defense than one ago, I would move him next season.
I hope that starting the season fully healthy would free his mind about past injuries and let him play real defense like he has the potential to.