Was Arnold the greatest of all times? Maybe not, but a strong case can be made that, given the distance between him and his contemporaries, that he was, indeed, the greatest ever. This is like the old debate between who's greater in chess, if Fischer or Kasparov. The latter achieved a higher ELO rating and was World Champion for much longer, but Fischer had a far more crushing superiority over his rivals than Kasparov: Fischer defeated Spassky at the 1972 World Championship in a far more dominating fashon than Kasparov ever dominated Karpov, Anand and Kramnik - his three strongest competitors. So if Fischer had access to the current amount of chess knowledge, he would arguably have a higher ELO rating than Kasparov and would defeat Kasparov in his prime.
A strong case can be made that no Mr.Olympia had the kind of dominance over the number two guy that Arnold had at the 1974 Olympia, not even Dorian at the 1995 Olympia or Ronnie at the 2003 Olympia. So going by this criteria, Arnold is the greatest ever. If he had access to current drugs and training knowledge, he would defeat a prime Dorian and Ronnie.
SUCKMYMUSCLE