What's your evidence that Sacred Harp style was imported by the English to the US.? My understanding is that Sacred Harp in the US started with William Billings, Daniel Read etc. in the 18th century, and many others in the 19th century. There is certainly a link with West Gallery--but the chronology appears to be such that there was cross-pollination--very hard to say who 'imported" what in what direction. William Billings, Daniel Read, etc did their work in the US--even partly before its formation. Billings' Chester--written during the Revolution--was in the running to be the national anthem--though it's quite likely that the line "New England's God forever reigns" did not help its chances.

It's certainly true that in the Sacred Harp book there are many tunes and lyrics from Isaac Watts, Charles Wesley etc. But the fasola style at least in its Sacred Harp pentatonic approach, as far as I know, originated in the US--it was in fact the first means of teaching music here--and many "singing schools" did just that---before the traditional (European) means of reading music triumphed.

Do you have evidence that pentatonic fasola singing in England predated the American Revolution?

I don't claim to be the ultimate authority--and I'd be genuinely interested if you have evidence of this.

In fact I would actually say that the rough--and pentatonic--style of Sacred Harp is more "Celtic" than English-- and there are lots of 4ths and open 5ths. And I'm saying that as a confirmed Anglophile.