I think archers work fine. In single player they're very useful.

The reasons they're not used in multiplayer
i) People always taking 16 units so they dan't want to waste a slot on a non melee unit
ii) Playing at high florin costs with heavily armoured units
iii) Using high valour units so that the morale effects of being under fire don't count for much.
iv) Use of large spear units that aren't that affected by arrow casualties
v) There's not much of that easy to hit cavalry around.
vi) Playing on flat maps with infantry rush tactics

Hopefully after the patch there'll be more cavalry and 60 man units around.
I've also changed the system so that the cost of missiles is not counted when deciding the cost of upgrades. This'll make combined archer / swordsman units such as Turkish Janissaries more effective.