Ill make the assertion, as someone who has taken Step I, and is preparing for Step II.
If youmanaged to actually get taught by him, you would need no other source to pass Step 1, that included pharm, anatomy, etc. Because he gives you most everything you need. If you are just reading the RR book, it is probably a little irresponsible of me to suggest that you shouldnt supplement RR with BRS or another small path source (i.e. not Robbins). Its all about minutia and different sources sometimes have different minutia.
I dont know the average USMLE Step 1 score, although I know that in my class (of 06) we had about 50 people sit for USMLE Step 1, and all passed. I think most of the scores were near the mean (with a few outliers), and I chalk that up to people preparing for two tests, and most of them taking the USMLE one to two days after the COMLEX. I think that last years class did well also, with only one person out of 88 failing board exams.
To top that off, what I remember for Step II from pathology class 18+ months ago is infinitely greater than what I remember from my rotations (maybe because attendings tend to give you their own advice, which doesnt always jibe with the national board's).
So there you go. He is enough, his info is usually enough, but one without the other and you might not get the full effect. He is brilliant, however, and needs to be seen to be believed.