I was a very lean 150 pounds when I started lifting in my early 20's, at a height of 5'9". About 5 years later I weighed 185 give or take and was about the same leanness. That's kind where it all tapered off and any weight I put on since then was fat.
The routine I settled on after trying all the whacky stuff was doing 3 sets of 8-10 reps and adding weight every so often, doing that twice a week for a particular exercise. Every so often I'd take a week off because i was tired, then I'd restart.
All the research I have done on natural weight lifters shows I was in the midrange for muscle growth. I still think adding 30+ pounds of muscle from weight training was pretty amazing, and I got a lot stronger to boot. But these chemical monsters we see on bodybuilding pages are so far outside the realm of natural that it is just a chemical freak show- and i watch them for the freak show thrill, haha.
I started at a low BF 155lbs and am now a lean 200lb onstage same BF % after 40 years training
If I was natural and the same BF % with training I would probably weigh 185
If I stopped training and maintaned the same BF% I would likely be 155 again.
We all end up back where we started eventually
Even pros end up back where they started if the stop training and taking hormones.
Imagine Cormier at 5% BF now untrained.