You're right. We will probably have more pains in the transition than we as fans think would happen. (Man, can't really image a season on CB with many, many bone-headed plays leading to a seasons with 7~10 losses instead of that many wins.)
One thing I disagree with you on is still BYU, or even Utah or TCU, in the first year being threatened with relegation. The results at the end of year one for Utah and TCU would not have cause either team to get relegated. And that would be the case for BYU. There are just too many "even worse" teams in P5 leagues that would be relegated before BYU.
Everything else I completely agree with...as a theory. Because, even if you end up being right, I would still go into the transition of being in a P5 conference with crazy fandom of still winning 8~10 games a year.
As a side note, though, this is a worthless debate as relegation isn't going to be implemented. So, whoever is right, won't ever be determined.