I wouldn't say generic mobs are undefeatable but the stagger mechanics combined with starred mobs and multiplayer buff for enemies can lead to a lot of 'learning experiences' where you perfectly parry the first blow from a new encounter and just one-shot detonate into a cloud of blood. There's not much to learn from that beyond "don't go there yet I guess" because there's no way to know if that blow was for 101 percent of your HP or 1000.

Honestly I could use some D&D style combat logging with numbers if the world's gonna be like that.