Do you know this for sure or are you speculating? The only piece of content about it that I saw was a video where the demonstrator used 20 archers and a single horse (before turn rate increased), he danced the horse back and forth, but it does not give me any clues as to how it would perform in normal sized battles.
My favorite idea for the concept was from @Jofursloft, he brought up the idea to have attack-ground just establish an area to attack, drawn by a corner-rectangle, and have the ranged units prioritize them. I am not sure how hard/laggy it would be to make each ranged unit target a random unit in the area, but I think using the current preference system (closest=best target) would be ok to prioritize the units inside the area.