Magic Might Sucks

Well, our party tried to attack Bob last night (see my earlier post for details on Bob). We barely survived, thanks to some misfortune (in some ways, deserved) and for a while there I thought I was going to be starting the Covenant from scratch by myself after I left the area. If it hadn't been for a last minute charge by some Grogs, that would have been the end of it. (Bob still lives, by survived I mean that we managed to pull everyone out)

This experience has led me to some ruminations on a facet of the Ars Magica system which I find to be.... well..... crappy. I think it is poorly designed and results in strange play outcomes. That concept is Magic Might.

Basically, for the uninitiated, this is a score possessed by a magical opponent. It is like a super-armor-class-vs-magic, typically in a very large pool. So large, in fact, that you basically have no chance to hit with your spells until the pool is depleted. And the only way to deplete the pool is for the opponent to fuck you up big time.

Now if they can be damaged by normal weapons, hoorah. Stab them with the steely death. Maybe you lose a Grog, but no mage is going to be long-term crippled.

But if they can't, because they are a ghost, fire elemental, rock golem, etc; combat might go like this.

Character 1: Cast magic, no effect
Character 2: Cast magic, no effect
Character 3: Cast magic, no effect
Character 4: Cast magic, no effect
Monster: Attack Character 4, incapacitate them (magic might depletes some)

Character 1: Cast magic, no effect
Character 2: Cast magic, no effect
Character 3: Cast magic, no effect
Character 4: Incapacitated
Monster: Attack Character 3, nearly kill them (magic might depletes some)

Character 1: Cast magic, minor effect
Character 2: Cast magic, minor effect
Character 3: Run Away
Character 4: Incapacitated
Monster: Attack Character 2, miss (magic might depletes some)

Character 1: Cast magic, major effect
Character 2: Cast magic, major effect, monster dead


Then you spend a year getting character 3 back in fighting shape because the wounds are beyond a low-powered character's ability to heal.

Meh....

I think the idea of a huge armor class of sorts vs magic is fine, if it reflects the inherent nature of the beast (ex. most Dragons). But the depletion thing would still be weird. Why is the dragon losing it's magic resistance because it is casting magic? Is it caught by the physics of conservation of magic momentum or something?  It causes this weird logic at the table of "well, lets just give him a few rounds of beating the hell out of us, and if we survive that, we can kill him".

Very odd. I don't like it very much (even though I do like the game in many other ways).

Thoughts? Am I overlooking some great facet of this mechanic?

EDIT: I want to also note that the player has no idea WTF the magic might of a creature is.