I think George Martin is being typically reticent. All you have to do is look at the kinds of producers who turned the Beatles down, not to mention the rest of EMI, to see that Martin is one of a kind -- a traditional producer who was a classically trained musician and also the kind of person who could help Peter Sellers do his weird work (check out the Indian My Fair Lady parody years and years before A Day in the Life and Harrisonia generally).   He was the one who could carry the Beatles through to the next level. In anyone else's hands, they would have developed into a very good Dave Clark Five.

My humble opinion.

yours,

Peter T.