I've noticed this to be a problem too. I'm not sure what the cause is but I think it needs to be tweaked a little.
The enemies seem to spawn closer and charge right at you, taking less time to hit your lines than in Warband - and I daresay less time than you would realistically have to pepper an opposing force with arrows (assuming you saw them coming). Then archers don't reliably fire, this could be a learning curve but I have yet to determine a good reason. Finally, when archers do fire the range is such that they have time to get only one or two volleys out before melee combat begins. Finally, headshots don't seem to be infliciting enough damage - it can take two headshots to bring a looter down from what I can see.