Well just from checking your gear that is likely alot of the culprit. Even capped at fifty your gonna be running with people that have gear that are at least 40 levels higher than what your wearing. So thats probably the bulk of your issue. From what you said of your rotation it seems fine, just make sure you pull with unchained up, SE > BB combo for initial hate.

Additionally, if you ran Leviathan uncapped... you wont have a prayer of holding hate on a lvl 60 DPS.