The biggest issue is the conference system itself, where you can't get true comparisons simply by who wins what conference.
Just as with the CFP itself, the ultimate factor is winning the game on the field. Otherwise, why not just vote for the "best" team? The same is true for conference championships. As long as the rules are set in advance, who are we to argue with them?
As noted, the College Basketball playoff system requires too many games to be applied to CFB. (It has also destroyed the importance of conference championships.)
The benefit of an eight-team CFP is that it respects major conference championships while allowing the inclusion of some other teams deserving special consideration. What is wrong with that?