I think, as I'm sure you do as well, that the claim that a Comanche warrior could shoot 10 arrows in less than 30 seconds from under the neck of his galloping horse and split a willow stick 10 out of 10 shots was an exaggeration.
What IS true is that every Comanche boy had been playing with/making bows and arrows since about the time they could walk, and had grown up in a setting where, in the absense of x-boxes, video games and TV there weren't a whole lot to do BUT practice the skills they would need as men (as William Penn said of the Delaware men 100 years earlier, "by their pleasures do they live", referring to hunting and fishing).
Furthermore the common expectation would have been eventual death in combat against enemies who were similarly adept (unless, possibly, they were going up against Europeans). The emphasis Indians commonly placed upon skill with weaponry was noted by many contemporary observers in differnt times and places, whether we are talking thrown tomahawks, blowguns, bows and arrows, smootbore muskets and trade guns through longrifles and repeating rifles.
With respect to bows, the COMMON level of virtuousity taken for granted in an old-time Indian camp was 1) bows were commonly shot by "feel", often held flat as Ford states, not by aiming down the arrow and 2) such things as knocking flying birds out of the air were considered not unusual skills.
Just recently I was talking online to an older Native guy who related that as Rez kids in the '50s', he and his friends would hit thrown quarters in the air with arrows for tips outside of bars regularly, and thats in the modern era. Well sort of, he did say his grandkids mostly play electronic games today.
Likewise, for Plains Indian kids who had begun riding about the time they walked, hanging off of a horse and firing under the neck would not be regarded as a particularly unusual stunt.
Hitting a willow stick weren't necessary, people are bigger than that. So, Ford's claim of rough parity could hold true. Dunno what distances/conditions those cowboys you mentioned were hitting rabbits. Unlike arrows, which could be used over and over and made for free by people with lots of time on their hands, bullets and powder cost money, a commodity generally in short supply among those most likely to need them.
But point taken that a guy who was adept with a revolver might hit another man on a running horse out to fifty yards, especially if he had five or six tries literally on-hand.
Jack Hayes is reported to have shot the head off of a rooster across the plaza in San Antonio with a Paterson Colt (while he was standing on the ground), and we know he personally had been using revolvers in combat for at least three years prior to the famous inaugural fight at Walker's Creek. The one comment though we have from Hays hisself on the topic of the correct range to shoot at while running after Comanches on horseback, that all sources seem to agree on, is that his instruction to his revolver-armed men trying this new mode of combat out at Walker's Creek was....
"Powder burn them!".Birdwatcher
