The key to Boss 2 and 3 is stun. You can stun the fire elementals that spawn and interrupt their flare casting which should keep you plenty busy and give you something meaningful to do since as you mentioned, the golem ignores aggro for the most part.

Same with the last boss. I would recommend pulling the boss near where the adds spawn out of. You can turn around and keep them stun locked as mentioned for 10 seconds which should be plenty of time for you and a well equipped DD to burn them down before they even have a chance to run after their target.