In trying to explain how the quality levels in various affiliations stack up... I finally think I've got a data driven illustration. The Power Ratings come from the Massey Ratings page and are based on 2019, but it's a great illustration of the diversity within each affiliation as well as how they kind of stack up (I think). It's worth pointing out that a team competing against an opponent with a Massey rating 2 points higher still has a significant chance of winning, so when you compare a team with a rating somewhere in the 5's with a team in the 7's (for instance), that's still a very competitive match...
The hype (https://collegeathleticadvisor.com/wp-content/uploads/2021/02/NCAA-Hype-Slide-1-scaled.jpg)
The reality (https://collegeathleticadvisor.com/wp-content/uploads/2021/02/WSOC-Programs-By-Affiliation.png)
I have always thought that a team's ability is not absolute, but in reality some kind of standard distribution.
Teams can beat anyone who overlaps on the two distributions. A team having a good day on their distribution can beat a team having a bad day. That is why we play the games.