True. But in the NFL, they have a scoring mechanism that allows the teams to decide who plays in the playoffs based on
wins on the field. And they can do that, largely because of the limited number of teams.
The CFP attempted to solve that via an invitation by committee - that's expected to continue in the new 12-team era. But as
@RonJohn so succinctly, pointed out, that always leaves room for bias:
IMO, bringing all the champions in allows for us to get the closest to what the NFL has - a mix of teams who are subjectively chosen by a bunch of people in a room, and teams that have earned their way in, playing it out on the field. And then we let them ALL play it out on the field.
As for your argument about a #1 vs. #16 not being compelling, I kinda see it, and kinda don't. On the contrary side, if rankings determined everything, Tech wouldn't have beaten Miami. Or North Carolina. Or Pitt. The list goes on.
In 2014, we were ranked #12 going into the Orange Bowl. We played the #3 Florida State team to the wire in the ACCCG. There's not a lot of difference between #12 and #16, and I'm confident our team could have beaten the #1 team that year.