That's an unreasonable request under the circumstances. Allen isn't here to play defense. He's here to play defense, shoot threes, shoot jumpers and be a guy you can go to with short time on the clock to get a critical point.
One out of 4 is not good. And in Game 7? I'm sorry, I'm usually first in line to defend a guy when he has a bad game, but Allen was too integral a part of the Celtics' plan to "give him a break" when he comes up this short at such a critical time.