Here is the typical thinking of muscleheads. I can't get any bigger so I need drugs. Damn, I can't get any bigger using those drugs. Conclusion: I don't have the genetics.
Look at Larry Scott. Poor genetics for a Mr Olympia. He persevered and trained brutally hard plus drugs and won twice. I doubt his physique could win today. But in 1965 he was a sensation.
The next year two truly genetic marvels appeared, (hearsay), namely Arnold and Sergio. Sergio more gifted than Arnold.