Great post. Here's a quick response:
I agree that a lot of people min/max. You make a good case for it and I don't think there's ever been a good argument to dispute it. I think Blizzard is aware of this as well. The problem is: you don't have to.
You showed that nearly 10% of players has done a +15. I think we'd both agree that a lot of them likely were min/maxing to accomplish that. What I'm arguing is that they actually don't have to. That content COULD be cleared without min/maxing.
Not long ago somebody calculated the amount of DPS the three DPSers would need to beat a +15 KR. This was done on the competitiveWoW subreddit. The number was surprising: ~35k. I can't remember the assumption they made for the tank/DPS (IIRC it was combined to equal one DPSes, so 35k combined in this case). Anyone who does keys will tell you this is SIGNIFICANTLY below the threshold most people believe is needed. Now, obviously this calculation assumed perfect play, no deaths, etc. But the point stands: people over estimate what is required. There's a certain air of "being carried by ilvl" in this game. Obviously you want better gear but the actual DPS requirements are far lower than people think they are.
It'd be trivial to make this calculation for any other dungeon: just total the health of a typical route and find the DPS required to beat the timer. An obvious objection is that there's movement and RP and all sorts of downtime, but the DPS is being compared Details / Warcraft logs DPS readings that already account for that stuff.
Another angle here is that of non-meta classes. The simple fact of the matter is that people are taking non-meta classes/specs, which is arguably the biggest form of min/maxing available, and getting them to high levels. You showed that only 1.11% of players are running +20s. Let's look at arcane mages and sub rogues who are by far the worst M+ specs right now. There's about a dozen arcane mages that have completed +20s in the USA. There's about 7 or 8 sub rogues that have in the USA. At a glance that seems shocking but both those classes have specs that some of the best in M+ rn; so, if min/maxing was less of a concern (and this post is essentially arguing that people rely too much upon it) then there'd be more people running those specs to begin with. But even the bottom of the barrel specs are capable of getting to a place only 1.11% of players have.
That's just looking at the absolute bottom of the barrel though. I don't think anyone would deny that you can be royally screwed by balancing in the game. It's also reasonable to think that Blizzard would have buffed arcane and sub in M+ if rogues didn't have other options (distinct from the locked-in covenants). Enhance shaman aren't that great in M+. Nor are Feral druids. Both have over 100 players in the USA alone in that top 1.11%.
The question we have to ask ourselves is how much do we actually need to min/max? I'm a mythic raider mostly in a near CE guild but I know HoF and World First guilds will rotate characters and then main the one they got the best loot luck on. That's a form of min/maxing isn't it? It's also something I would never engage in. I don't want to nor do I think it's needed for my WoW "goals." I reckon this is true FOR MOST players. In fact, I think your data supports the fact that you don't need to min/max to achieve the things you likely want to achieve. You just need to #GitGud.
You ended your post with a potential counter argument. I'll do the same and it's one that personally aligns with how I play WoW: I actually greatly enjoy min/maxing and pushing my raw DPS as high as possible, simming, and all that jazz. Min/maxing is a playstyle that isn't necessarily about pushing content.
TL;DR Totally agree with OP that far more people min/max than just the "1%" but the deeper question