many of those sampling heavy American music styles (hip-hop, much electronic music) were very directly and strongly influenced by Jamaican dub which grew out of reggae.

I think the argument is reasonable that we don't get any of it, at least not in the forms we have now, without Jamaican music. DJ Kool Herc was Jamaican.

on the other hand, it is definitely true that the American music industry with its strict copyright has not exactly been stagnant. but it is different.