@cor3zone
As someone who's gotten hit before in a fight (well, "fight"), taking more damage doesn't mean you shift your attention from the person in front of you, for the simple reason that shifting your attention involves getting hit *again* by the person that's already in front of you. It's way more effective and efficient to take down the currently visible target before moving on to a different one, otherwise you just get disoriented and things get bad.
Like...taking martial arts, the first thing you get taught is some variation of "don't lose focus, don't get flustered", because the instant you do your defense is gone, and that's just a bigger invitation to get hit. Focusing on a new challenger seems like it's losing focus and, in this specific situation, I don't think Garm is newbie enough to just stand there as the monster looks around for who just backstabbed it.
Also, considering the whole "two dangerous attackers" business...shouldn't it be "three dangerous attackers"?
I mean, the distinction between a 'tank' and a 'dps' character doesn't exist in the real world. If you're getting hit, then the person doing the hitting is dangerous, pure and simple. The idea of having damage work as a means for a creature to determine threat level is a wholly videogame-world idea.
Animals in the real world have tusks n'shit for the sake of intimidation, because the entire point is to be dangerous *before* the fight starts. Once it starts the relative level of danger stops mattering: one good hit and you bleed to death, nothing stopping it. No HP bar to drain, and all that.
To put it in a different way: when I was sparring with a black belt I knew he was dangerous BEFORE he kicked me on the side of the head, not after, and if you were to ask me whether if his or his brother's kick felt harder I could honestly tell you that I was too busy in pain to judge. I mean, I can tell afterwards that his brother kicked harder (dude was heavier) but in a life-or-death situation I would likely not be alive long enough to make that kind of value judgment.
Anyways.
If the party had a mage then I feel like the show would just be over at that point, since the MC would have his raid party and just rumble through everything.