Net accuracy depends on the weapon, the experience of the user, weather conditions and, in the case of cavalry, the movement of the user.

The chance to hit depends on net accuracy, the range to target, initial and final projectile velocity, target velocity, target size, target density, special projectile properties (body-piercing, bouncing, area effect) and the presence of obstacles.

The lethality depends on chance to hit, attack power, target missile defence and whether the projectile is armour piercing, flaming, launching and/or exploding.

Air resistance is not modelled in M2TW so projectile speed does not decrease.

It's true that projectile properties are largely independent of the shooter. In fact, with some simple modding you can create Vardariotai that shoot cannonballs or musketeers that shoot naphtha bombs at 200 m/s.