Yes, Miners have armour piercing. Yes, Miners have 80 armour. But they also have melee stats almost at the level of Peasant Mobs. They lose against all other chaff infantry of their price, I think something needs to be done here.
I already hear everybody saying: "but Miners can hold a long time to give missile units time to fire!"
But here is the point.
What is dangerous to Dwarf missile units? --> High mass monsters. They just smash through your lines and ping pong back and forth through you back lines.
This also means that Miners do nothing to protect your missile units! Chaff infantry kills them, and monsters just terrify them away: They don't even have Immune to Psychology!
A Dwarf thread a day keeps the chariots away.