Well, part of the problem with your thoughts here is the language you're using. Nobody said there's a "genetic problem" ... more that those who CAN run a sub-5 have a genetic advantage. And that seems reasonable to me.
If we set 4min as a standard of elite athleticism, how does 5 mins look?
5mins/mile is to a 4 min mile what a 12.5sec 100m is to a 10sec 100m. I sincerely doubt that the average male could ever run a 12.5 100m, regardless how hard they train. Certainly a lot of men could, but you're suggesting most of them? There's no way in he**.
I think it just comes down to the disparity in natural talent. Think of what the very top IQs are, and then suggest that with the right education, the average person could score a 150. Or an absurdly high SAT score, for example.
I taught guitar for a long, long time. "Good" students might progress reasonably rapidly. But ... the average person, with an awful lot of training, can barely stay in time. I think we'd be surprised if we really how broad that 'talent' curve is.
When I watch the OG, for example, I'm reminded of how exceptional these people are. 2:05 marathon? That's inhuman. A sub-4 min mile statistically doesn't even exist, and you're suggesting that those who CAN run that time aren't really that much better than the average human. And that's ludicrous.
A 6 min mile would be 'average' for men with a lot of training, imo. But there'd still be a whole host of guys who'd simply never run under 6:30. Ever.