You are not wrong on the facts but I don't agree with the conclusion. One of the best stretches of basketball in recent history was when the core line up was:
Smart
Brown
Tatum
Horford
RWilliams
All the same players. Look at W-L, NRTG, +/-, whatever you want, this team/unit was great. It made it to the finals and lost to a very experienced GSW team. RWill was not the same last season, not sure he ever fully recovered from his knee surgery, and Horford was a season older and kind of faded at the end, but these guys were not all that different than the year before, maybe down a little. Marcus Smart was the same Marcus Smart. I think what happened is the team got in a funk when it was announced that Udoka had accepted a job in Houston. All the tension with the players around that seemed to kind of flare up. We went on to lose 3 straight to MIA. Of course them having scrubs that shot like Hall of Famers didn't help.
I agree that all these things were weaknesses and they all have been fixed or improved upon. We have Holiday for Smart, Porzingis for RWill, and Horford in a role where he won't need to provide as much offense. I completely agree that these additions are going to make a big difference and now the whole Udoka thing is 100% in the rear view mirror. Now if everyone can stay healthy and keep focused on the task at hand, the sky is the limit.