Rainman, I'm on my iPad, so will address in detail tomorrow. But population aside, you're missing the "Divine Spark" and "unique" aspect.
In musical terms, there's been only one Elvis. One Johnny Cash. One Jimi Hendrix. One Brian Wilson. One Eric Clapton. One Chuck Berry. One Mick Jagger. So on and so forth.
There are more kids playing football today than in the 50's, 60's, 70's, 80's and 90's combined.
Yet, where are the multiple Johnny Unitias clones, Joe Namath, Steve Young, John Elway, etc.?
You can add cities and players. But that doesn't mean that the talent level will remain consistent. Given the facts above, it'll be further watered down.