I just want to say your point about Orlando losing 1mill Brits just doesn't hold up to scrutiny (yes I know you exaggerated but i like debating
). Simply because for a Brit it's a very different thing from taking a daytrip to Bedford than it is going on a full-blown holiday to Orlando. UGB could never truly cannibalise visitors from UOR simply because people aren't going to Orlando exclusively for Potter (well most people, the Potter stans definitely are), they're going for multiple things which the UK could never offer even if UGB was a carbon copy of IOA.
I do think though that the discourse that not having Potter will have a severe blowback, simply because I have confidence that Universal will make sure UGB opens with an IP on the level of Potter (they could even open with it) that will draw the Brits in droves. Whether it's LOTR, SNW or something completely new, it'll be a big enough deal to negate any Potter blowback.
What I think is happening is alot of Brits are very excited they might get WW in the UK (to the level of Hogwarts Castle/Hogsmeade) and the idea of it not happening has people fretting and worrying. Sure there's the Studio Tour, but honestly it pales in comparison to the IOA WW, just for the sheer impact and awe it inspires.
In my own opinion I'm of the mind that the best route they can go is pairing that big IP with Potter, that would definitely make a statement. Now whether they go HC/HM or some other location in the WW I have no idea but I think having a properly themed WW area and another huge IP is the best way forward. But that's just m