Here's the thing though....would that have made sense in any of those cases? I get that this is the Phil Mackey talking point, but it's incredibly surface level.
Kirk Cousins would've taken that franchise tag, signed it, and happily played under it. Goodbye Greenard. Goodbye Gink. Goodbye all sorts of options. Plus another year of Kirk. And by the looks of it we damn sure wouldn't have got anything for him this year.
Hunter would've meant no Greenard, no Gink, no FA contracts. He might've also stayed. Maybe you could've squeezed someone for an asset, he's the best case for it. But it would've come with costs.
And Darnold? Time was on his side. If his agency didn't like the tag and denying them free agency....they could refuse to sign it, taking the cap room from the Vikings, and slow playing their interest in being moved. The Vikings miss out on free agency, have a disgruntled player eating 40M, and watch their market for a return shrink.
Basically, if the player and their agent don't want to play ball.....there is no ball to play here. The only way this would've worked is one of Darnold's pursuers want him badly enough to start trade talks. It sounds like that didn't happen.