Other problems with issuing threats to someone with unknown superhuman powers aside: I feel like they're potentially underestimating how fundamentally fed-up with bullshit someone who's already been stuck in a loop for 12 years might be.
Control over my own life would probably be just about the number one thing I would be relishing, which you might well have to pry from my cold, dead fingers before I would relinquish it.
On a more devil's-advocate sort of note: I disagree with the people who say that Ares is crazy for trying. With the limited information available, there's a decent chance that neither of them knows who's got the advantage here for certain—especially with the magic stuff up in the air. And the protagonist's personality is largely unknown to everyone: It's not-totally-unreasonable for their guild to try to get a hold on him early with strong-arm tactics, before he's had a chance to test himself against the rest of the world... Like, obviously not a smart move, but not as dumb as it seems to us (who know he's the protagonist and know pretty much for certain that he'll win in any beat-down situation).