As i said, most of game mechanics are "RNG" like, but none of it is actually random.

And this is the case for most cRPG games i know. Or maybe people who dont like it would want a 100% chance to do anything.

Physical and magic armor are going to be either a hard invulnerability barrier you need to chip away to Zero, or some sort of soft barrier. And percentage based is one reasonable easy way to do it. Which is in line with the rest of the game mechanics.