Well the thing you might have missed is that this is in powerlifters who are elite and "specialists" already, guys who are truly maxed out naturally. No lesser expert than Charles Poliquin threw out that quote about 10% vs night and day in bb. Also if you gain a ton of weight on drugs it will affect strength more vs staying pretty much in a weight class. My friend went from a 300kg deadlift to 330kg in the years he juiced. Depending on how you looked at it that could be considered huge. I went from 130 x 1 on incline to 180kg x 2 on my first Dianabol cycle. That's a 115lbs increase for double the reps 
Some "experts" opine test doesn't even really start working in a PED kind of way until 250mg due to some type of level having to be reached. I don't think that's really correct. Watched a young guy at the gym get on legitimate TRT and the change was insane. He was truly hypogonadal and he was truly in normal range after the Nebido was put in since this wasn't a "longevity" or "sports TRT" clinic.
well if I take myself as an example I think I pushed my own natural limit as close as I could I think as my progress really slowed don and did not move from like 27-30 even thouh I tried to push it. I did get up tp 315 for 5 reps bench as best naturally but that was being 15 kg more fat on me than Id want. getting fat being in a big calorie surplus helps alot for a natural trying to push strength.
then at like age 40(due to not training seriously for many years(kids/life etc.) I pushed my strength up to 315 for a single at much leaner bodyfat. Then I started the test and got to 360 for 3 reps after like 4 months on 250-300 test ew.
So for me even though i wash probably pushing my natural limit the increase was still 15%.
regardless I see many examples that speaks against what you say about elite lifters pushing limits naturally not gaining more than 10%.
Take Pete Rubish. Deadlift specialist. Did 900 deadlift I believe(maybe slightly more don't remember). And that was on test and tren, on pretty high dosages.
He then went cold turkey off gear. Documented everything on youtube. Did everythign he could to get his natural test levels back, which he did manage to do. And then tried to push his natural numbers. His deadlift naturally, around 600... So naturally his Deadlift is 2/3, or 33% less, than of that on steroids.
I think from everything I see and gather from my own experience now and what I can see honest people do achieve on gear vs off is that lifting and bodybuilding is highly androgen level dependant.
You remember "True Adonis" on here, he pretty much coined the phrase "all drugs", and that is sadly... very true about bodybuilding and powerlifting. Sure training and diet has a part too but to a large extent pushing dosages is likely very much a thing.
Tbh the biggest "black pill" for me was the autopsy report of Dallas Mcgarver. He is imo probably the strongest bodybuilder(successfull one) ever, AND his dosages where in the autopsy report extreme. 10 grams.... The correlation of dosages and strength/size there is hard to not see past.