They are not going to bench Pierce for Green.
Pierce is the much better player.
Yes, and equally as important, Pierce has great chemistry with the starters.
Our team's biggest strength was its starting unit. I remember reading that our starters, as a unit, had the best +/- of any unit in the NBA this season. That being the case, I'd be hesitant to break them up.
Rather, I'd like to see us improve our bench. Ideally, we'd find some post scoring, rebounding, and some increased athleticism.
Incidentally, moving Pierce to the bench doesn't instantly help the unit. The vast majority of the time, Doc had Pierce or Ray playing with our bench. It didn't help matters much. We don't need to change the lineup, we need better players.
Additionally, moving Green to the starting lineup in part takes away one of his bigger strengths: his versatility. Right now, he can fill both the small forward and power forward roles off the bench, depending upon matchups. That is potentially valuable, if Green plays to his potential.
I think part of the solution -- beyond just finding better players -- is for Doc to mix his bench in a little better with his starters. There's no reason to substitute the entire bench in at once; I think the team would play more effectively if Doc tried to keep 2 or 3 starters out there as much as possible.