They can still score because Pierce has stepped in admirably to handle some of the distribution that Rondo normally handles.
It's a great aspect of the team that they're able to handle these kind of problems, only a real veteran team could do what their doing right now.
Defensively, Nate at high minutes hurts you, there's no question. He just does not have the length to bother people, although his ball pressure is great. If he goes under the pick and roll, he's dead in the water, he cannot recover quick enough to contest, because he just doesn't have the length. Even straight pull ups off the dribble generally get of with a full hand length over his outstretched arms. Yes, he has the vertical, but he has to be careful in timing those jumps without contact, very, very difficult to do.
I love Nate's ability to create, I love his tenacity and the energy he plays the game with, but more than back up PG/Scoring punch off the bench, he will never be.