Through my lifetime, a lot of musicians from the UK have done extraordinary performances of classic blues from black US performers from the first half of the 20th centuries. Most have used an accent that sounds quite American, and I think that's quite appropriate.

Same for singing Country songs - works better with an American accent.

And then there's Lonnie Donegan. He sang lots of American songs, always in an unmistakable Lonnie Donegan accent.

Accents can be very effective - if they are done credibly.

-Joe-