Empusa probably does demand a longer fight. Possibly her first 30 seconds she can take only 25% of the damage done? No One should have trouble targeting her since it's just one boss. Hit tab and shoot something. It can be a bit challenging for an all melee build though, to get through a large scrum.

Some people do have bad zoning times. CC has a known issue, for whatever reason, and it does take him and a few other people time to zone. (But how did you miss HF?The portal stays up an hour and it's long, long fight.

Too much loot I'll argue is just poor planning. You know how much you can get if you take all gems. Unload before bosses start.

The adds are problems on two fights: Claudia and HF. You can avoid a lot of the problems by simply avoiding the adds. On Claudia, don't run up the hill, and stay away until Claudia spawns. On HF, die and stay in town until HF spawns. If having difficulty tagging a boss with melee, load a ranged skill no matter how lame. I've used Cold Ball with one character. And if you die after that, you can usually reload skills before the boss dies.

I expect that as we get more optimization done, there will be less need to turn down graphics. People with bad computers and connections will still have problems with that many people, but I expect things to get better. I don't see a hell of a lot that can be done about this by the programmers just to fix an event. We just have to live with it, it's beta.