I'm adjacent to everything, going so far as to have gotten the mythologized locker room talk about where to find stuff. I keep abreast of discussions about models, athletes, and actors. Even the movie Icarus comes to mind about government agencies overseeing doping programs.

As a rule of thumb 1) I think the world of muscle building can completely FUBAR a person's understanding of what they can expect from natural lifting. 2) you can ask yourself simply: "does this person have a financial incentive to be strong/good looking?"

The idea that you can be afraid of building too much muscle is exclusively in the realm of endurance athletes, someone with a coach and nutritionist, or someone with a very particular and narrow band of self-image.

To that end, I would never be surprised to learn that an Olympic medalist of any stripe was using some kind of designer chemical that mirrors some androgenic effect of whatever testosterone byproduct. It's probably a billion dollar industry and prohibition is simply ineffectual

At least 25%. Probably closer to 4 in 10. I'd bet WADA has some statistics that are probably pretty accurate.