I've come up against some especially tough monsters. 5 of my party members almost always miss, and 1 almost always hits! He's a Half-Orc Knight (the default, Tyro. Yes, I know I'm boring). All of my party has really close to the same Accuracy (all roughly around 20). The Half-Orc has quite a bit higher Might and Speed than anybody else, mostly from gear. I can only guess that's related to hit chance, somehow.
They all carry quite nice weapons (gold, quartz), so that can't be it.
You'd think I'd know this by now but... hey I don't! :D

Even more important than might for hitting is the number of attacks per round your characters get.
The monsters you met obviously have armor class so good that 2 attacks per round are not enough to get through while your knight gets enough attacks and does too much damage for the monsters' AC to absorb.

Aha, I think I understand what you're saying.
So does the game count 4 attacks as one giant hit, or 4 separate attacks? I can see the latter being extremely powerful, and it would explain a lot. Even if it was separate attacks, I guess I could see my knight passing the AC, anyways, since he's so powerful.

Assuming it works like the earlier games in the series, then it's 4 separate attacks, each with their own chance to hit. That's why it's such a big advantage against high-AC enemies.

EDIT: Nope! See kmonster's post below.

In MM3 and WoX the 4 attacks are added together to one giant attack before damage reduction from monster armor is applied.

Aha! My mistake (I edited my post above). It sounds like AC reduces damage taken rather than making monsters harder to hit?. Although maybe if the monster's AC stops all the damage from an attack it registers as a miss?