The top 2 teams are head and shoulders above every one else, number 16 probably lost 2-4 games and is not in the class of the top 2. FCS, DII and DIII can get away with larger playoffs because there are even fewer out of conference games or games out of your region played. Because of that, it's hard to get a feel for how good a team is compared to the top teams in other conferences. In FBS, you can pretty much figure out that Alabama and Clemson are in a different world than App State, Boise State, Miami (Oh), Florida Atl, and Memphis by looking at common opponents since there are usually games between conferences.

I used the 2019 conference champions above, and App State only lost one game to GA Southern, well GA Southern lost to LSU 55-3, so you could expect that kind of game in a 16 team playoff. Boise St lost 38-7 to 8-5 Washington, Miami (OH) lost 76-5 to Ohio St, FAU lost 45-21 to Oh St., Memphis was the high point losing by 14 to #10 PSU in the Cotton Bowl.

Let's face it, a 16 team FBS championship playoff would have most of the first round games be blowouts, there will be 10 conference champions, Notre Dame, and then a bunch of teams that lost the conference championship games and then some 2nd place in a division teams.