United does not have a hub in Fort Lauderdale.
It is in the process of building one after Spirit's bankruptcy and increasing regional demand. United is starting a direct flight from Los Angeles to FLL and is planning on using FLL as a base for flights to Africa and increased service to the Caribbean. Also, if United can push for a people mover to connect the airport to the nearby Brightline station, that would open up the entire Central and Southern Florida region via one United hub.
I agree with everything else you said.
The problem with MCO is that Orlando doesn't want a hub airport. The entire economy is based on tourism and having a hub doesn't help unless the hub is owned by the government.
FLL needs a new tenant who could treat the airport like a hub. Delta has ATL and American has MIA. JetBlue has a presence there, but likely not enough to fill the lost capacity unless it gets a massive capital injection. That leaves United and Southwest.
United is the airline that has the quickest ability to fill the void and has a long term route strategy which can use an airport like FLL, including off-loading some international traffic from IAD.