All of BGW's major coasters were on 2 trains (except Tempesto), the issue was a combination of low staffing and poor procedures which resulted in excessive loading times. This was compounded by:
1) station layouts which resulted in 10-20 people waiting for each row for most coasters (not an issue on Griffon, dreadful on Tempesto)
2) lots of exit guests being sent to rows at random rather than to (a) specific closed row(s).
As a result, whilst queues didn't look long, you could be stuck in the station for absolutely ages. Having proper merge points and/or only having 1 group waiting in the bays for each ride would have improved the guest experience significantly, even if the throughputs were no better.
I think RAP is becoming more of "a thing" in US parks nowadays, not yet to the levels of UK Merlin parks but it seems more widely used than my first major US roadtrip when it was just wheelchair users. It's only really a problem where parks have bad operations anyway.