First of all, Nobody is becoming a pro fighter if they don't train at all. Of course, you have guys that Are naturally gifted, And can get away with less training, but that extra athlethicism has a lot to do with higher natural testosterone levels, focus And self esteem. All these go through the roof when adding for example some synthetic testosterone. No natural ability can compete with that, And on top of it, you get in 2-3 times as much training.
I am not at all saying that everyone can be professional fighters by roiding. What I am saying is that the naturally athletic guy that is not using peds will fall so far behind the naturally athletic guy training beside him using illegal peds, that there is no way he will even make it past amateur levels.
After year 2, 3, 4, 5, the guy being able to train more than twice as much, And even being able to fight 3-4 times a year, will have so much more experience And be so much more powerful that they will never be on the same level.