ToME: the Tales of Maj'Eyal

why do arrow quivers have significantly less ammo than packs of sling shots, like twice as less? how is it balanced?

A pouch holds more than a quiver?

I always assumed the balance came from the fact that, on the whole, bow/arrows usage is somewhat more effective than sling usage for various reasons, so having larger limits on sling ammo compensates for that.

but how are slings so less effective to deserve to have two times more ammo? i haven't played a slinger myself but as i remember slings and shots i saw in game weren't bad at all and slingers can use the same key archer skills - aim, steady shot, scatter shot etc. they don't have piercing arrow skill though, is it the reason?

To be honest I think ammo count is kinda pointless.

It doesn't prevent npcs from endless spamming stuff at you but it's a constant annoyance to the player without any actual interesting gameplay mechanics.

Actaully it does; npcs are bound by the same rules as you are

It actually made early Skeleton Archers a lot less annoying, honestly.

I just assumed it was a flavor kind of thing. Bow archers get more skills that hit multiple enemies (dual arrow, piercing, scatter, volley) than slinger (who only gets scatter shot). And the increased number of shots allows slingers to make somewhat better use of rapid shot, which can be pretty amazing, while archers are probably more inclined to take Aim.