I agree with tehlegend. I've previously used a rapid insertion force to great effect against deathwing and the same concept applies to the retaliation cadre. This is the kind of thing Farsight's mont'ka style is made for, hard hitting counter strikes. Deathwing can't stand against massed plasma for long especially if they aren't the close combat storm shield variety.
Belial himself does carry a storm shield which will make him harder to take off the board than his friends but he's still by no means difficult to kill if you're equipped for the job.