

M1 Abrams: Requires an advanced economy plus an army of General Dynamics contractors for maintenance
Trebuchet: Can be completely repaired by one hammer-wielding villager
Plus, I assume that tanks count as a cavalry archer unit, which means any old monk can start converting them. Meanwhile trebuchets can’t be converted until your enemy researches redemption at the monastery.
Not a Polish film, but Hard to be a God (2013) is that.
It’s a 3hr B&W Russian film about futuristic scientists who are living on a medieval planet to study it. Everything is disgusting, claustrophobic, and filthy (the main character is a germophobe). As he watches a fascist theocracy take control of the kingdom, the protaginist wrestles with whether or not to get involved.