that's a very good idea Quinn Inuit and CC, I was suggesting to CC to make them recruitable over 2 turns to make them less OP but this idea would work even better.
btw, isn't hydaspes considered an exceptionally bad performance for the longbowmen or am I confusing with the chariots ? Arrian (IIRC) says that the longbowmen anchored the bows on the ground (although I have no clear idea how this actually works) and they found it very difficult to do it in the muddy banks by the river.
coming to these specimen, the main difference in technique was that while other archers drew the strings up to their chest, Indian archers drew the string alongside their ear, this was the main reason in difference in drawstrength. I would suppose a 1.5 multiplier to time between shots as compared to other archers should do the trick.