You answered your own question
The younger US audience don't care about lyrics at all no more. Raye a singer but the few songs she rap, on she got better bars and flow than the Instathots they promote as rappers here.
Central Cee just by having some cleverness and rhyme schemes on a higher level than most in his age range here. For me, he too shallow with his content most the time and don't switch up his flow enough, but he got talent.
I don't know if I can even list an American rapper under 30 that emphasize lyricism and content at all and is actually popping. The ones that's actually nice get pushed to the side. shyt is sad.
At least the UK recognize the younger acts that speak on real shyt and put effort into the craft lyrically.