I see all of your reasonings, but I still think the Marvel contract was much bigger of a deal in the late 90’s/early 2000’s.
MCA signed that contract for a song, before Marvel started cropping up more in theaters (with multiple Spider-Man, Fantastic Four, and X-Men films, and even the Hulk film in 2003). It was a huge get for them, and led to one of the best and more well-rounded lands in the park... at least, after Storm Force was added, there was something for almost everyone.
BUT! That was several management changeovers ago. Comcast came in, the US resorts began being marketed together, and Potter is the new Golden Goose (at four Universal parks, for now, at least).
By contrast to Potter, Marvel Island looks dated and stale, a reminder of the 90’s design philosophy of slapping some cut-outs on a building and calling it “themed” (Toon Lagoon’s King’s Row, USH’s CityWalk, and the Shrek 4D/Dispicable Me streetscape in USF being just as guilty of that). They can’t use the design or look of the popular films, or the now-relevant characters in them (certainly not Guardians).
And they haven’t successfully built a brand-new ride in that area since 2000 (Storm Force)... the rumored Iron Legion Ride is awol, and at this point (with Iron Man probably not surviving/retiring after the first or second Infinity War film), they kind-of blew their window to make that really appealing. Maybe they wouldn’t focus on Iron Man, but the suits... but then, that seems like a huge stretch to me.
So that means MSHI is essentially a “time capsule”of a land. Sure, they’ve updated Spider-Man’s ride films (and made the music dubstep... see how well that ages...), given updated costumes to the walkaround characters, and rebuilt Hulk (which I maintain, would stick around with new themeing if they give up the contract). It’s not a good position for Universal to be in.
Black Panther, now the most successful film at the box office, remains in Marvel’s library, unable to be used by Universal in any meaningful fashion. And even if they quickly pitch a new ride for those characters from the film (or their comic counterparts), there’s no guarantee that it would get greenlit by Marvel. And even if it did, they would have to retheme it to clone a ride like that anywhere else.
I just think Comcast has bigger plans than that. It’s one small corner of the park that has a contract that could be potentially worth millions (billions?), versus Disney’s deep pockets and willingness to buy out a contract to achieve parity with DLR. I think it’s worth discussing and theorizing on.
After all, both resorts would win here. Disney would get Marvel, and Universal would likely redesign the island to fit something else. Maybe even demolish Spider-Man for a new multi-level space, like Nintendo Land is said to be. I’m just spit-balling, but overall there is so much to gain by dissolving this link between Marvel and Universal (and that’s coming from a person who worked in MSHI for two years, and loves the place!)