But you're not doing that! You're still letting them (or the coaches, or the journalists, or some humans somewhere) pick the teams. They're just picking more teams.
I still can't tell what your objection is.
If it's to undefeated G5 being left out in favor of "media favorites," just change the rules to keep them in, so that undefeated teams always get the nod over teams with losses. Then your problem only exists if we have 5 undefeated FBS teams, which I don't think has happened in my memory.
If it's to one conference getting two teams in, just change the rules so only conference champs get in.
If it's to one one-loss conf-champ getting excluded in favor of another one-loss conf-champ, then we can create "on the field" metrics to determine which is the better team (wins over ranked opponents, margin of victory, offensive and defensive squad rankings, etc.).
There's like a million solutions to these problems, other than giving Wisconsin get a third chance to beat the same Ohio St team!