If size alone won contests then Paul Anderson or Ivan Putski would be multiple Mr. Olympia winners.
Granted Zane wasn`t a huge man, but still had plenty of muscle on a small frame,great proportions,top notch symmetry,defined quads that most others in 1968 couldn`t come close to matching,a finished/polished look to his build and a very pleasing look as well (NO HOMO),plus he was a great poser who knew how to display his body to accentuate strong points and hide the weaker ones.
Sergio had insanely awesome genetics but got beaten mostly because he was never quite in top condition, except I feel he got robbed in `72,but if he had the cuts to go along with his great mass and God given genetic shape, not many could have touched him on stage.