I think the C's largely lost this game becasue they shot 20% on open threes. If you shoot 20% on the kind of shot your team is best at at making, you are going to lose.
Everything else is sort of window dressing. I know the three point shooting thing annoys fans, but the C's offense is largely built around their 4-8 guys being able to make shots. White, Horford, Holiday, Hauser and Pritchard all derive MOST of their offense value form hitting three pointers, and KP Brown and Tatum derive at least a fair amount of theirs even if they can do stuff inside the arc. If nobody can make a shot your offense just isn't going to score enough to keep up with great teams.
The thing about the C's is the reliance on threes means they will occasionally lose a game and it will look terrible, but are they going to shoot 20% from three 4 times in a 7 game series? Probably not. That's the hope anyway.