Something that I noticed is that the AI doesn't seem to like to block with shields in Bannerlord, so I'm not surprised. If they fixed blocking like how the AI did in Warband you'd have totally different results. When you tell your units to go to shield wall and advance towards the enemy, recruits still die a bunch while tier 2 units with shields do not. Why? Because they're blocking with their shields at this point while the recruits don't have any. So in conclusion, if the AI knew how to use shields then they are very effective against archers. Your test does not take that into account.
Also the fact that recruits weren't slaughtered in melee though proves that shields are in fact a great addition because fights against recruits are less of a steamroll you guys seem to want to keep around.