This deal seems like a terrible idea. The Celtics will be worse next year, not better, because everyone will be a bit older. That was inevitable. So maybe you take one last stab at it with the core group.
But now that Celtics have a huge salary albatross in years 3 and 4 of the Pierce deal. That seems like a bad idea for two reasons:
1. Even with an aging Pierce they'll win more games than they would have won without him, which means a lower draft pick, e.g. lower chance at a franchise player through the draft.
2. Takes up salary room and makes the Celtics less of a free agent player.
Additionally, Pierce's "game" does not seem well suited for a backup role. Can you imagine him being the 4th fiddle on a Celtics team 4 years from now that miraculously got more young talent?
Sorry for the negativity, but I'm not sure the relative improvement in the change of winning a title next year (versus not having Pierce) is worth the disaster that will strike years 3 and 4.
Maybe Ainge is planning to leave so he won't have to deal with it?