Well, my position on "Brits singing American" is that it is not the truth!
It's a bit like these "tribute bands"; they might be fine musicians but they are copyist, and if they wanted to make a "true" musical statement then they would have to find their on voices.
I must admit, I want to laugh out loud when I hear Brits singing in these pseudo-American accents.
Of course, the Americans themselves have a history of young well-educated white kids ( John Hammond Jr, for example), trying their best to sound like some black chap from 1920s/30s Mississippi.
It's all very entertaining, but it will never be the real deal.