The act 2 boss in Drednaught

Act 2 boss says its vulnerable to cold, But I have walked thru act 1 and 2 and I do very little dmg to the boss. I am using a frost bolt and nova build and I would assume I would be doing more dmg than I have been thought acts one and 2 up till this point. Is he not not vulnerable to cold? Is this a bug?

I have the same experience i am lvl29 and using frost bolt. I picked every possible cold and spell damage. Everything was going smooth and I didn't struggle until act2 dreadnaught boss. My damage is extremly low agaisnt this boss or boss has too much hp idk. I can't even get it to half hp. I tried 10 times and simply stopped playing. The amount of loot we are getting in the campaign is extremly low. We need frequent better gear drops so we can feel the progression.The game feels so rewardless right now. I am using lvl 13boots in lvl29 because i couldn't find any decent one. I couldn't find in merchant also. Trading shouldn't be way to go until end game. We should be able to self sustain in campaign in my opinion. Passive points refund should also be free until end game.

This boss specifically I think has too much HP for current game form.

It becomes a too grindy fight, easily twice the count lenght