i think they are legal realists and have no theory about legitimacy being important. they do not understand that others have the option not to follow their commands and think that they have access to an infinite well of legitimacy.
Which makes me wonder to what extent the SCOTUS Republicans are just doing a more genteel version of Trump's core fuckup: they think they are now our Guardian Council and have no idea how to actually build legitimacy for authoritarian rule, ignorantly leaping off a bridge thinking they can fly.