What you just listed is nothing new. Alabama had a coaching change and still almost made the playoff the first year post Saban. Clemson lost forehead slap games and had close calls when they were dominant, see our win in 2017. Michigan was meh for years before Harbaugh and meh this year with him gone. USC has been inconsistent since Pete Carroll left. Washinton is not and has never been a factory. They had a magical year and fell back after losing their coach. Oklahoma fell back as soon as Lincoln Riley left. Georgia almost lost to an in state rival with a winning record. That's not proof they've fallen off.
What I see with the teams you listed is more influence by coaching changes than the portal. And as some factories have dipped a little, other factories have stepped into their place, Texas and Oregon.