I think it's debatable now, after the March 2 Nets game. It seems quite possible that the reason the Cs' offense sometimes (some would say 'often') bogs down is... everybody, especially Rondo, sometimes (some would say 'often') falls into the trap of dribbling the ball on the perimeter while Allen dives all over the court through multiple screens looking to get open. Ray's absence seems to open up the offense for the starters, so that there's more aggression going on, from everybody. Pietrus also provides sufficient spacing compared to Allen, so even that will not be missed.
And the defense is clearly better with Pietrus replacing Allen. It's not even close. And as always, better defense leads to better offense.
I think it's time to start contemplating Ray Allen coming off the bench. For real now.