Peake the Harvester is an unbelievably unfair fight. I would even say it's entirely impossible to do while leveling in Realm of Discord. The amount of health regeneration he has, combined with adds with shields to block your attacks against him, combined with his INSANE damage (500~800 dmg hits on lv 15 me with 1200 HP), makes this the most unreasonable boss fight in the entire game hands down.
There are no effective strategies that can be done here outside of maybe being level 100 with Tier gear. Any damage you'd do with leveling gear will be healed in seconds. It would honestly be extremely impressive if you could get his health down by even 5000 (53k HP @ lv15).
So Salan if you're still out there, it would be amazing if you could nerf this guy. The adds are fine just disallow him from 2 shotting anyone, and remove the life regen (Or drastically lower base health). The Life Regen he currently has probably puts his effective health at well over 200k @ lv15 if you were able to just stand still and straight dps him.