How about this:
First, reduce accuracy of low tier bows by quite a bit, increase accuracy of longbow and slightly increase accuracy of rus bow, but increase draw time of all bows. Essentially the goal would be to make the longbow the best bow, and to make it about as accurate as the horn bow is now, but it would be slow so that you don't get people machine gunning with it. EDIT: Just something I forgot to mention, change the accuracy "sweet spot" to be later (preferably differing for each bow, such that maximum accuracy occurs a fraction of a second after fulling drawing the bow)
Second, make all bows 2 slot.
Third, make quivers for arrows and bolts be 2 slot but give them 50-100% more ammunition. This is for 2 reasons, first it means archers will have to use the 0 slot weapons, even for low tier bows. The primary reason for this is that as bows stand now an archer with a low tier bow can, if they want to sacrifice a bit of ammo, equip themselves with a fairly decent 1 slot weapon. This evens the melee field out for archers, additionally it means that if someone wants to use a 1 shot kill machine like the arbalest, they need to sacrifice nearly all melee ability. It would make high tier crossbows be for dedicated xbow only, and make it so that they can't whip out a 1 slot weapon and start dominating in melee. If an xbow wants to be able to melee, they should use one of the lower tier xbows.
Finally, make bows and xbows deal reduced damage under a certain range, which reduces further the closer the target gets. For example, 10 meters would be the shortest distance where they get 100% damage, then for every meter closer reduce damage by 10-20%. It's unrealistic, certainly, but could help reduce one of the major complaints about these weapons: shotgunning. No matter how good a player is at dodging, at very close range it's practically impossible to reliably dodge bolts and arrows, and at these ranges the archer/xbow should have to pull out their melee, or run.
The goal of this would be to make archers have to be a bit more careful with their shots, without really nerfing the good archers, and to make high tier xbows have to sacrifice their melee ability.