Pierce has been like this throughout his career. It appears he's coasting, but then when you least expect it, he hits a dagger, as he did last night.
I accept the argument that his shot is flatter than ever before in his NBA career. I think it's that way because he's buying into the team scheme more than ever before. Paul Pierce's bad habits usually re-assert themselves at some point, now you basically never see "too much" 1 on 5 isolation out of him. He's a matured pro now.
Knowing PP, It's just a matter of time before he kicks his game up a couple notches and people regret ever saying anything bad about him.