well guess that puts to bed the argument that casters go right through them that I've seen posted so much. Oh maybe it was only casters at epic levels with ruin/greater ruin spells that do untyped damage.
They have prr AND mrr. Their prr and mrr go up the longer the live. They are also immune to mental effects like mass hold.
This makes it harder for BOTH casters and melee.
Both casters AND melee have ways to get around this.
Players have been sharing info on how to get around this since the event started, but are ignored, or worse yet, called "elitist jerks" for offering advice. And I'm not talking about difficulty settings.
Advice is useless if it's ignored. The thralls require a different strategy for most people to be able to handle. If you refuse to adjust your strategy (which may require build adjustments so you can perform the actions required to implement said strategy) then that's on you. Of course they'll still be tough if you refuse to do anything required to deal with them.
1: kill them first and kill them fast. They do not start with 5 stacks of their defensive buffs. They start with 0. The longer they live the more stacks they gain.
2: split them up. They gain stacks when near other thralls as well. They lose stacks when split up. This may mean grouping with other actual people *gasp* or using CC
3: physical crowd control works very well. for casters this means things like web and soundburst. For melee this means things like Stunning Blow, Trip, etc. CC in DDO does not make enemies more resistant to CC (like D3 does as an example), do you CAN spam those abilities (no cost for melee) to keep them locked down permanently, split them up, and widdle them down without getting hit back.
4: use damage types that ignore prr/mrr. Untyped and Force. These damage types are easier to get with casters, but they are not exclusive to casters. Melee can get access to those for their weapons as well (shadowblades)
5: use Instakills. Most thralls are not immune to instakills. Instakilling doesn't just mean finger of death and similar spells, it also mean vorpal (which is a melee thing).
6: patience. sometimes it's advantageous to retreat to heal, regroup, re-plan, and try again. A thrall with 5 stacks - once they lose aggro/stop attacking - will eventually go back to 0 stacks. One can use stealth and distance and line of sight to lose agro and let the thralls calm down. Then you can come back fresh, maybe with a different strategy (like stealth+bluff to lure them to you one at a time if it's a group), to take them down much more easily.
Those 6 points do not guarantee success every time against every possible encounter, but they ARE options to make dealing with them easier. It is not "elitist" to point this out. But if one refuses to even try any of the above, that is (imo) on them.
edit: again, I'm not saying the thralls are not difficult, I'm not saying they don't make the game harder. They do. Is the amount of prr and mrr they gain per stack perhaps a bit too much. Yes, I do think so. But that doesn't mean the above ways to adjust to make them easier do not exist either. Doing the above mitigates much of their difficulty (not all of it, but much of it) and makes them more manageable.