Dawnseeker, breaker, ... one of the developers said they want us to have the fun of discovering how things actually work on our own, so they won't answer questions like this. Actual, I kind of respect that.

I assume that you have read one of the mage posts, in one of them there are some strong assertions that the crit rune won't cause a mage to crit, but does cause the mage to do the higher end of their damage range.

Things can block mage attacks. Bosses in particular. So break does help. Lots of speculation that some of the misses we see with mages against npcs are actually blocks that the game just shows as misses.