I don’t think he’s acting rationally - Elder Dragons can’t be tamed or controlled. Don’t you think it’s funny that his objective (to be in a position where he has enough power to rival the Pact and/or Aurene) dovetails nicely with Jormag’s presumed priorities - namely to put the brakes on the dragon-killers that Aurene and the Pact represent? Given that Jormag is the most subtle Elder Dragon, I doubt that that’s a coincidence. He's not trying to tame or control Jormag. He saw the Kralk's power can go to Aurene and intends to do what Charr do best and fight a war against Jormag. I'm not saying he's smart, he's going to get slapped hard and do a Scarlet style thing where he triggers an Elder Dragon. But he legitimately thinks he can win, and winning wins puts the Charr ahead of the other races.