Erm... I wonder dare I ask the obvious...
Are you actually playing the server and experiencing these mobs as the community are?
To be frank everything you're experiencing was for the most part copy pasted by Jeff from my own work, which i have extensively play tested but realized there are some issues yet to be determined.
My goal is to make the mobs with a few things in mind, since we did have a sort of Design Theory behind them all:
1) They should be taking no cactus damage, and half of normal lightning, poison, and fire dot damage. They should also be taking around 10% of explosion types of damage.
2) We realized early on that if we do not set their combat distance to be their AI distance that anything with ranged can easily solo all the mobs. Further into this we realized that its still possible to just jump up two blocks or whatever distance required and still cheese the mobs. We decided to give bosses a "combat distance' wide aoe force teleport to prevent cheese mechanics. We initially set the CD of that teleport pretty high to keep it chaotic for the players. People who keep their cool will realize it's not too big a deal as the mobs usually also have (on cooldown) abilitys that easily avoidable.
3) We wanted to make some of their ability if not most of their abilities avoidable. By this, I mean things that are going to utterly kill you. Minions, which are mobs that are summoned, usually have a decent health but should be taking twice the damage as a regular mob. So, if you focus them, they should die pretty quickly, and lower the risk factor. We also decided to take the time to make these mobs have either ranged or melee attacks depending on how the boss feels to balance out it's damage range.
4) We wanted to introduce basic faction-like mobs and then have bosses that summon minions, and use magic or spells and have cool particle attacks and be really hard if you simply didn't understand that they're designed very much in reference to common MMORPG dungeon bosses. As I've said, most should have avoidable high damage attacks. The bosses regular damage should be tankable by any warrior path or maybe even a healer.
5) Threat tables are wacky right now, but I can't fix it. Threat = whoever has registered the most 'hits' on the target mob recently. I have yet to determine what 'recently' is defined as, but this seems to be the rule of thumb. If you have a class that has a lot of 'ticks' of damage, this will generate a lot of threat on our mobs atm. With this in mind, DK's or things with lots of dots and direct damage swings could probably suffice as a tank with proper heals.
6) We also wanted to experiment with charge/leap/throw among other skills, like consuming other minions for HP and things like that, to present different challenges. In theory, however, if anyone has read any 'raid guides' there's a general strategy that works for almost all of them. Stay out of the poop.Whelps, left side. and the classic.. MOAR DOTS!!
Haha, I hope this clears up some things as I am in charge of designing, maintaining, and helping balance mobs, which is why I'm open to suggestions, but please let this be a reminder to the community that I am not here to make things EASY. We very much want things to be quite difficult. Ideally, balancing the line between fun/rage quitting. That's just being honest. That said, our line for that is pretty reasonable seeing as how people rage quit pretty easily. As belisarius has stated above, our biggest goal was to provide a challenge (not impossible barriers) to people who play in their towns or what they think was safe. The randomized (mini) boss spawns are absolutely great for this. But, because they're randomized they will not have great loot or be as hard as a normal boss found in dungeons, and we will make them despawn after time so they don't just camp places. So, now we will set them to either 1) despawn when out of range, or 2) have a hard-set 20min timer to remove the mob out of existence.
I'll keep staff posted on updates to this in the development area of the forums. I am open to dev suggestions there as well (I have openly tagged and posted there asking for feedback), since the other staff can playtest on live. Also, I have been randomly selecting players to whitelist on the alpha server and summoning them to arenas we've built to playtest the bosses and/or new mechanics as max level/fully geared (but not enchanted) heroes.