Ranged units are problematic for balance. Humans, you see, are very good at maximizing ranged power. The AI is less able to take this advantage. This is likely why standard bow weapons are so incredibly nerfed. I can use ranged units and retreat to the very back to get 2 strikes in before the enemy can catch me. That might seem powerful, but bows need to stand well balanced in normal tactics. That exploit is not a logical basis for nerfing. Let's look at the figures for bows versus staves, shall we? A shortbow takes a tech that only gives shortbows. That is somewhere around 25 turns on average to get a single weapon. The magical staves also offer a variety of other weapons, buildings and items. So you get alot more just from choosing the magical choice. The difference is that shortbows take only labor to build. That means you can mass produce them without having alot of resources.
Now let's look at damage. A shortbow does 7 pierce damage with -8 Initiative penalty. It weighs 10. A staff does 6 fire or ice damage with -6 Initiative. It weighs nothing. Compare this to the weapons from the prerequisite tech for bow, Weapons. You can get 9 melee damage with backswing from an ax at only -2 Initiative. It will take you a turn or two to reach the enemy, but in that time no bow units will have even fired. Add a wood shield to that and you have one powerful unit. In tests, 4 axes with shields and full leather beats out any combination of bows and axes. You do very little damage with bows against even slightly armored units. The following bow techs offer only a single bow weapon and are not too much better than the one before. The best bow you can get for trained units is in the Magic Tree and you don't need the other bow techs to get it.
I have to conclude that bow weapons are not useful as they are outclassed by staves and do nothing but clink against anything as good as chain armor. Tarth has a few slightly better bows, ending with a wonderful late game bow that ignores 50% of armor. Other than that, you are better off with melee or staves. Ideally you should get axemen and then staves. Once fire mage group with two axemen groups is pretty much a free lease on clearing the lands of monsters. Bows never compete, unless you have zero resources and are desperate for some defense.