I take issue with the following statement

"It's not as if any of the top 8 teams, in almost any given year, would be considered "unworthy" if they had two playoff-quality wins to close the year."

The more playoff rounds you have, the more likely it becomes that a three loss (or more) team could be crowned national champion over a one loss team, which, assuming the one loss team had a legitimate schedule, is a plainly unjust result.

If we go to eight teams, we're also almost certainly including conference champs, which all but guarantees an entirely undeserving team will be given a chance to get hot and win the championship. The 2008 Super Bowl is a prime example of something that should never happen in college football. The Patriots went 16-0, including beating the Giants at Giants Stadium during the regular season. They rematched in the Super Bowl, and the Giants gave the Patriots their only loss of the year, in a 17-14 game. On balance, there's no credible argument that the Giants were a more deserving recipient of an award for the NFL's best team that year. The only credible argument is that they won they playoff tournament. But this result makes plain that the NFL playoff is not a good vehicle for determining who the NFL's best team was that season.

Nor would an 8 team playoff in college be a good method for determining who college football's best team was that season. In 2016, putting 10-3 Wisconsin in the same single-elimination tournament as 13-0 Alabama would be plainly unfair. Let's even suppose that Wisconsin had beaten Alabama in the first game of the playoff. Overall, Alabama's performance would still be more impressive than Wisconsin's, even if Wisconsin went on to win the next two games as well. 13-3, versus 13-1.

In short, any single elimination tournament purporting to determine a season champion that could create a scenario where a win by Team A over Team B that would not result in Team A having a more impressive overall season should be invalid. An 8 team tournament fits that bill in college football.