The cannon part is the most annoying. I rarely see any groups breaking up after that. Most groups (that actually break) seem to bleed there. I don't know why but there seems to be damage spikes there. There's a guy (not the one that goes green and explodes, that's very obvious) that knocks you back and you either suffer some ridiculous damage or not. I can't say what enemy is that or what kind of damage he does but it can be evil sometimes.
i actually haven't seen any groups break at that point but im pretty good on turret so if im not on my tank to start with i'll hop on an kick whoever is the tank from the turret spot. the turret helps a ton and i see it used wrong alot of time, ie shooting one mob and letting the rest beat the living daylight out of the heal/group. btw he is bloated something or rather and he does 8-10k aoe before u add in armor and shield stuff bout. a dps should lead them away from group but the main focus should be on screamers and mercs for their ablities