With my limited knowledge on the subject (resulting from some research I did on the “One Percenters” motorcycle gangs that arose in the US and Canada largely sprung from War Vets that were trained in the War), I think the US use of motorcyclists as dispatch riders was rather limited due to the success of the Jeep and other smaller four wheel vehicles. They were certainly used and motorcycles saw action in all theaters, but they were limited and really didn’t play that big of a part despite the romantic aspects…
The “trick” you saw with the rider using an M-1 was more likely a demonstration unlikely to be useful in combat. And motorcyclists were never useful as any sort of neo-cavalry any more than horsemen were. They were however extensively trained and from what I saw had to undergo a rigorous training program riding over rough terrain. Some were used as perhaps pickets or for recon, but they had limited usefulness in combat, even as runners. The resources allocated for bikes were better spent in Jeeps and other four wheel vehicles which could carry more people and cargo…