But, yeah, the non-initiated get a pretty skewed picture about how muscular one can get, naturally. That's a whole another discussion about body perception/dismorphia and societal idealizations.
It is also fairly easy to give an accurate estimation (esp. if fat percentage <10%) via FFMI.[0]
In some natural bodybuilding competitions anyone with FFMI >25 is ruled out automatically because of the high probability of steroid use at that point. Of course a non-trivial amount of natural genetic freaks certainly exist beyond this number and a case can be made that's the whole point of competitive sports: "freaks" competing against each other.
But then again once you are in the highly competitive game it is (nearly) impossible to resist PEDs.
I guess for that reason many different classes/federations exist to choose from.