Funny, I had the opposite experience.

Boone, ED-E (yay companion limit exploits!) and myself destroyed the Giant Radscorpions in that one pass where they are all clustered. In fact, I didn't really do much of anything. The two of them slaughtered them before I could even bring up V.A.T.S. the majority of the time.

I'm playing Normal and not Very Hard, so maybe that's the difference.