Basically, with your idea, most G5 teams don't ever deserve a chance at winning a championship. With what you are saying, we should just change the rules and only let the P5 teams be their league -- remove all the G5 teams that the P5 doesn't want to invite, like possibly BYU.

The reason for including a MAC or Sun Belt champion, instead of a top 10 team, is that they actually won their league. Why should a team that can win their conference championship be able to win the National Championship? Sure, most years they won't have a chance winning in the playoffs. OTOH, I think you underestimate some of those teams. Sure, they are likely to lose but I don't believe they would get blown out in their first games -- and there is no way we will know until we let them play. And they would generate some excitement, just like the Cinderella teams in March Madness -- and some that are frequently successful, such as a Boise, could end up shedding that "Cinderella" label. They also, just like some of the small basketball teams, likely improve since they could now actually play for the championship. One big issues for G5 teams is that recruits know they won't ever play in a CFP, so they should go to a "real school" if they have that option.