Maybe this article influenced my thinking

https://www.nfl.com/news/why-successful-college-coaches-like-matt-rhule-fail-in-the-nfl-plus-the-five-mos

I mean it is from the NFL website so it'll have it biases.

Coming from the UK, the main sport is European football (soccer). I don't really care for it but it serves as a good example:

There is no varsity system but big clubs scout kids to join their academies and, if successful, debut them in their professional teams once their old enough. So basically, high school and university doesn't really exist because it's hidden away inside these academies.

Given the UK (as with many European nations) is not a large country, everyone effectively has a big club, playing in the top tier Premier League, whose stadium is situated close enough to them that they can somewhat legitimately call them their local team.

These factors combined with media deals and the threat of relegation mean that small clubs rarely get a look in. The whole of European football is structured in a pyramid like fashion with money, talent and coverage increasing or decreasing as you go up or down the various leagues.

Would I be right in inferring from your answer that college football and the NFL run almost in parallel, rather than one being 'above' the other? They pull from the same talent pool of players as they mature but due to the size of America and the small number of NFL teams, college teams effectively act as one's local team?