And, let's just look at the 3d6 bell curve for a second. That gives a nice, gentle bell curve. But, populations don't look like that. Probably something like 90% of the population would be between 8 and 12. And you certainly wouldn't have 3% of your population with an 18 or a 3. That's ridiculous. The reason we baseline at 10 is because that covers about 90% of the population.
It's the other way around; it's not that 'the strongest guy in the village/town/country/world' is defined as having 18 Str, but that 18 Str defines the strongest guy in every 216 people. You don't need to make any claims about 'Str 18 is Olympic level/strongest in the village/trained/not trained'. The claim is simply that, statistically', 1-in-216 people in the general population have 18 Str.
The remaining 10% can pretty safely be ignored. But the notion that a given population should follow a 3d6 bell curve is not supported anywhere in the game. Yes, the range is 3-18, fair enough. But, that does not, in any way, presume a smooth distribution through the range.
If we apply the same criteria for evidence to either case (and we must if we are to retain credibility) then we must compare the evidence for the claim that 'the general population is modeled by the 3d6 bell curve' against the claim that 'we know NPC stats range from 3-18, therefore they are nearly all exactly 10'.
To support the bell curve case we have the 1E DMG, the 'common ancestor' of every version of D&D from 2E onwards. We also have publications like The City State of the Invincible Overlord by The Judges Guild for D&D 1E, which lists (I kid you not)
the entire population of the city(!) with stats rolled on 3d6 in order! Why? Because that's what the general population
is! And they had the time to do it.
The reason that later editions had pre-rolled stat blocks for 'commoner' NPCs is
not that the underlying assumption of the bell curve was dropped but that a.) the couldn't be bothered to roll tens of thousands of stat blocks, and b.) they realised that they didn't
need to, because they can pre-create representative stat blocks that the DM can whip out at need.
And, let's not forget, [MENTION=6799649]Arial Black[/MENTION], while you're claiming that all sorts of concepts are available if we die roll, it's not actually true. The "I trained like crazy and now I'm an Olympic level athlete" isn't actually available to a character that starts with a 19 or 20 stat, which, your method easily allows for. That character didn't train at all. After all, isn't the claim that die rolling follows natural talent?
It is a ridiculous to claim that 1st level NPCs have
zero training when they already attained their 1st level class features! Along with backgrounds, this demonstrates that 1st level PCs combine some training alongside their natural abilities. This doesn't mean that they can't train even more. The 1st level PC with zero XPs is a snapshot in time of the life of that person; before that point they were less trained, after that point they will be more trained.
Which means all your olympic athletes are actually just born that way. They could sit around eating donuts and playing Xbox all day long and they'd still have an olympic level physique.
Which just demonstrates the maxim: Garbage In, Garbage Out. If you start with false assumptions (1st level PCs have had no training) then it's no surprise that you reach a false conclusion (Olympic athletes were born with exactly the same abilities as they have when they compete, so baby high jumpers can jump just as high as their adult selves will be able to jump in the future).