If we want to be realistic, then a bow of the sort used in Bannerlord, penetrating high-quality armor (lamellar, double mail over padding, or especially coat-of-plates) in 4 hits, is far from it.
We have multiple historical accounts, backed up by modern tests, of 10+ arrows being fired into padded mail with little effect. The Byzantines in 1108 wrote how they could not make an impression with their arrows on the mail of the Franks; the Arabs in the 3rd Crusade wrote of how they would shoot tens of arrows into Crusader infantry, with the arrows actually sticking in the mail and getting caught in the padding beneath, and they would keep advancing at normal pace without breaking ranks. In some cases, armies survived multiple days of constant arrow bombardment thanks to their armor. Armor was expensive, it was annoying to wear, but people wore it despite that because it gave good protection!
So the most realistic course of action is to increase the protection that armour provides. Even if it's just to, say, 7-8 hits to kill rather than 4-5.
From a gameplay perspective, nerfing the accuracy of bows at long distance is not going to fully solve the problem of
100% horse archers/
90% archers, 10% infantry being the strongest and best way to play, because:
A - When you have a block of 100 inaccurate ranged units shooting at a formation of 100 advancing infantry, shots that miss to the left or right of the intended target can still hit a guy on the left or right side of him. If there's a height difference involved, even shots that go too high or too low for their intended target can still hit the guys in front or behind! So accuracy nerfs have to be pretty harsh to make a difference.
B -
100% horse archer strategy is still OP. You just tell them to hold fire until they are at close range, then circle the enemy while shooting - you're uncatchable, and you're shooting at close range so long distance inaccuracy changes nothing.
C -
90% archers and
10% infantry strategy is still OP. You put archers close behind infantry in loose formation, hold fire until the enemy infantry is attacking your infantry. Now the enemy infantry is clustered around with their shields down and backs to your archers, at close range, so long range accuracy doesn't matter.
Both infantry and archers will kill in 4-5 hits,
but infantry get in each other's way, and can be blocked by melee swings. So while multiple infantry are attacking 1 infantry,
all your troops are attacking
all enemy infantry without interruption.
Even if your infantry die, your archers in the center of the line become the next melee distraction, while your archers on the left and right wings keep shooting the enemy infantry.
If we nerf accuracy and the AI's archers are staying at a distance as usual, they will be missing more shots - so the accuracy nerf may actually make this tactic even stronger against balanced armies!
Here's an illustration:
(1 - Enemy has 5 melee troops fighting at reduced efficiency due to melee block, and 5 ranged troops fighting at reduced efficiency due to distance inaccuracy. Player has 1 melee troop fighting at reduced efficiency due to melee block, and 9 ranged troops fighting at full efficiency.)
________A A A A A
.
.
.
________IN_IN_IN
________IN_IN_IN
.
A__A__A__A__A__A__A__A__A
(2 - Enemy has 2 melee troops fighting at reduced efficiency due to melee block, and 5 ranged troops fighting at reduced efficiency due to distance inaccuracy. Player has 2 ranged troops fighting at reduced efficiency due to melee block, and 7 fighting at full efficiency).
________A A A A A
.
.
.
__________IN_IN
___________A A
A__A__A________A__A__A__A
To change this scenario, you would have to make T5 archers unable to consistently hit a guy a few meters away, to a frankly unrealistic degree. And why do that when you could instead buff armor, and make it act more realistically?
Making arrows do less damage against armor is the solution.