Probably comes down to the x-men, bc even tho a MCU F4 might get the hard core geeks excited, we're at a point where mainstream audiences aren't really checking for these vanilla white superhero movies in bulk. Likely why Marvel did preemptive strikes with race-bending Spidey's supporting cast and Valykrie in Thor [and Idris], to avoid that stigma and show inclusion.
Miles but more so Kamala [women of color are arguably the most neglected demo in superheroes, when it comes to actual being superheroes] has an untapped potential because she's essentially the MCU's version of Pixar's Coco waiting to happen, but with a Muslim family. A big family movie about culture, with laughs and cameos from other marvel superheroes.
FF was the foundation for marvel comics, the property has been handled poorly tbh, although their most important appeal is for their associated characters/worlds; its still a desirable IP; add in the X-Men/Mutants, and there is no reason to rush Kamala or Miles into the MCU for one big reason. Money; If Disney is spending 50+ for Fox best believe their going to be at the forefront of the MCU simply because you don't spend that kinda money for those IPs to sit on the Shelf.
Regarding diversity, you just made the point, with now Okoye, Shuri, BW, Valykrie, Wasp, and Captain Marvel (and if the rumor is true Monica Rambeau as well??) the MCU's WW, they'll have their female slate bulked up and if you add in mutants as well there's not going to be as much pressure on that end anymore.
Miles isn't going to happen for a while since their def going to get all they can from PP, so unless their is some multiverse fukkery (and I doubt they just do that for a one shot), MM is going to be a wait.
Kamala is strange. I personally rather see a Kamala movie than a Carol Danvers, but you really can't rush her in. She's a big CM stan, and is also a inhuman, which seems like the MCU has thrown in the bushes. So you'll have to re-do her origin somewhat if they're not going to introduce them.
This leaves America Chavez. I think she might be the best bet to introduce since her origin story is kinda weird and you'll have more free reign with her and she hits the superhero box that hasn't be pushed (latina).But
TLDR; Disney paying way too much money get fox properties for the MCU to prioritize MM, KK, and AC at this time.