There were maybe 100 people who took drugs and took bodybuilding seriously in the 70s. Arnold just happened to be hungrier than the others. The rest of the population didn't.

Quite possibly so
The same can be said for many other sports & pastimes in those days
The winners & champions were still the best amongst their peers
its no their fault there was not much competion.
Though with Arnold / Sergio even to this day there are not many who can compare.