I have a feeling the main problem with a lot of bosses, not just synced ones, is the companions being too insanely strong.
I am redoing an agent for the DvL event, as an operative. I havn't done this story in, oh, 2 years or so.
I just fought Jadus and I decimated him. I absolutely wrecked his face. Everytime he stepped down off his platform, he just got MELTED in a second and a half. Jadus used to be HARD, not just challenging, HARD. You saw people asking for help on DK, fleet, alderan, for help to fight Jadus. I mean that guy whooped my butt repeatedly!!
Now vector slapped him in his face and he died.