We've discussed it already. The top black British actors are classically trained and have extensive theater experience. From Idris Elba to Damson Idris and everyone in between. Many American actors came from New York acting schools at one point but television has opened the door to less trained, less "professional actor" actors over the last couple decades. For every Jonathan Majors, who is classically trained, there are handsome men and attractive women who can't really act but get hired because they fit whatever Instagram image the show wants.
You can scroll through the casts of BMF, Power, most MCU shows, etc and see a lot of American actors who didn't go to school for it. That's not to say non-classically trained actors can't act. Joaquin Phoenix is arguably the best actor right now and didn't go to acting school. But when you're auditioning against classically trained actors who are used to doing Shakespeare you're gonna lose that audition unless you're really fukking good. And a lot of these young American actors today aren't...that good. You see it in the acting you see in shows and films they're in.