I definitely think there is a lot more demand from Disney "refugees"--I'm one of them--visited Universal twice in 2021, first at Portofino, then Royal Pacific. Next trip staying at Sapphire Falls. I'll upgrade to a premier for the right price, but not at $600. I don't think I'd be willing to pay much more than $400 for them. I am the kind of person willing to pay $600 for a deluxe at disney though, and here's the difference:
(1) At disney deluxes, the rooms are large and almost all of the deluxe resorts comfortably sleep 5, with "real" bedding for all (as opposed to the $39 a night rollaway for the 5th person at Universal that barely fits in the room and makes an already quite small room uncomfortable cramped).
(2) The disney deluxes have more of a transportation benefit relative to the disney mods and values--the deluxes often are walkable or have boat transportation compared to bus only at lower tiers. That means it feels more than a true upgrade than at Universal, where the lower-priced hotels are all pretty convenient to the parks--and sapphire falls even has a boat.
(3) For at least some disney fans (including me), who are used to parks that are more about the atmosphere than the rides, and attractions that are not really "thrill" rides, the express pass is a nice to have but I'd be fine without it. I don't do coasters that go upside down, and a lot of the rides were a bit too ugly/scary for me (Mummy, Jurassic World, Forbidden Journey, and Kong especially) and the more tame stuff felt too geared to kids (Minions, Seuss, Transformers Spidey). The second time we went to universal, I basically only did four things: (1) Hagrids, which doesn't even accept express pass (2) Gringotts, (3) Flight of the Hippogriff, and (4) just spending time in the Wizarding World playing with wands, snacking/drinking, and exploring shops. I realize this is not everyone's experience coming from Disney, but I don't think I'm alone among the Disney refugees--there are a lot of people like me used to just hanging out in World Showcase having a low-key day, exploring Pandora, or wandering out Galaxy's edge with a ronto wrap---or, importantly, just spending a day without a park ticket at a deluxe resort--who don't really put a huge value on express pass.
I don't question that there is a ton of demand for the Universal premier resorts now because everyone is coming over from Disney for the first time and premier seems like a natural choice to people who view it as Disney deluxe accommodations but with unlimited fastpass. But I don't think it'll last. With the exception of Wizarding World, nothing else at Universal appealed to me in the way Disney does. Wizarding World along is good enough I'm going back in a couple of weeks and likely will be back again to use my annual pass one more time, but I definitely won't be paying $600 for a premier hotel. I'll stay at a lower budget one or stay at disney and uber to universal for the day.