Are the PT and merc your DPS classes, or is the PT the tank? It's a pretty well knon fact right now that PT tanks put out more DPS than Juggernauts, which may also be a problem.
All I know is, the first time I ran HM BT, we had a Sniper and Assassin and all the bosses were loot vendors. Ran with a Vengeance Jugg and fresh 50 Merc (dunno the spec) and got eaten the next time.
actually now that I think about it, we have hit one enrage timer which was " Sith Entity" or w/e the bonus boss is called in False Emperor but between sabreward and my trinket i have an 80% chance to avoid damage so we just ripped the last 4-5% down w/o me even taking any damage.