Realistically it is no harder for a bow to be shot flat-trajectory than any other weapon. The arc only factors in at longer ranges because of the slower velocity.

There is even a small adjustment for rate of fall in good rifle sites. And modern artillery is fired in arcs with angles as large or larger than those of ancient bows.

..

As far as the game issue, it seems clear in this case that the longbowmen are just a little bit impetuous, whereas the arbs suck at melee and therefore stay out of it.

Dunno though, haven't played MTW.

Del