I have zero love for the Big Ten but I disagree with your assessment. If we’re just going off who can win a national title, then yeah it’s a down year for the Big Ten, but even then they have more than Ohio St. Penn St, USC, Oregon, and maybe even Nebraska (look at their schedule) could all be playoff teams. But when we’re talking about realignment, year to year isn’t that important as you can discount Michigan’s value just because they are down a little a year after winning it all.
To your tier list, sure, the Big Ten has 5 blueblood or near blueblood schools in Ohio St, Michigan, Penn St, USC, and Nebraska that the Big 12 has no chance to match but they also have another 5 schools that would still clearly at the very top of the upper echelon of the Big 12.
You might be able to argue that Oregon, Washington, Wisconsin, Michigan St, and Iowa wouldn’t be number one in the Big 12, but even if true, they would absolutely be in the top quartile at a minimum.