Nobody is saying that you take steroids one day and wake up the next an amazing fighter.
But if you don't think performance
enhancing drugs can give a fighter major advantages over a clean dude, you are delusional. Advantages in the fight, advantages in how hard he trains and recovers.. why would guys take them and risk bans/fines if they were not hugely beneficial.
There's also the case of very average fighters who had lucrative careers due to PEDs. You think Shane Carwin would have made it to the UFC if he had not been juiced to the gills during his regional career? I would bet good money against it.
He was an extremely mediocre fighter skill-wise. The only thing he had going for him was that he was friggin huge which made him a heavy hitter and very marketable aesthetically. He made a tonne of money and even fought for a title. All thanks largely to steroids. Maybe there was a talented clean fighter who could have had the spot if it wasn't for cheating scum like Carwin.
So don't try to dismiss them like they have no effect on performance or even career earnings. These juiceheads are getting ahead via cheating.