Okay second of all, defilers this update are in no way like minstrels last update. If anything, they're more like yellow captains. They're just PITAs who run around not dying, saving other people you're trying to kill by giving them a clutch blessing or stacking the hell out of HoTs on them and laughing at the majority of freep inc healing debuffs because of http://lotro-wiki.com/index.php/Fungal_Spores 's passive buff. There's only a handful of certain inc healing debuffs that really hurt them. They can also tank a dozen unskilled players, or an entire keep, and laugh at them while trolololololing around.
Just like yellow captains used to run around perma-bubbling against unskilled players who thought they should just spam skills at the yellow captain until his health goes down, or saving freeps who were soooo close to death, and in essence, just being a pain in the ### for creeps in general.
Neither class could kill someone who wanted to live. You just run. That's it. You turn around, press W, and ta da, you don't die to the defiler/yellow captain. *Input Staples commercial*
The only difference is that defilers can be defeated by focus-firing them with inc healing debuffs, while yellow captains were defeated by largely ignoring them in general in raids (as their CDs were long and could not be reduced quickly without being focused by creeps or NPCs) or bursting them down within seconds.