The volume 3 offense even when the Cs aren't close to making them is something that is not sustainable.
This group are so mentally soft that when they don't fall they quit.
Again, this is not only wrong in a basketball sense but at a base statistical level. You CAN NOT stop shooting because you miss shots. If you do so you are doomed. You may also lose if you keep shooting, but this team WILL LOSE if they stop shooting them.
There has to be a balance when they are not falling. You have to have a plan B to pivot to.
Let me re-phrase what you are saying: When the Celtics best offensive player is out and their starting center is in foul trouble and their threes aren't falling they should have a way to generate enough offense to overcome a team who themselves is shooting 40% from three in the game.
That's not a plan B, its a plan D.
At some point you run out of counters. There are very few teams who will survive their bets player being out, their starting center unable to play because of fouls, and getting outshot 40% to 31% from three.
And yet they are still only down 6!