I'm a juggernaut tank with about 15.7k hp unbuffed 25% defense, 40% shield, and 25% absorb. I have cleared Battle for Illum, False Emperor, Boarding Party, BT, Directive 7 all on hardmode.
I use my cooldowns according to enrages and abilities. The thing that makes these instances possible is the wise use of cooldowns and coordination within the group.
Yes, these instances are badly tuned
Yes, they are very unforgiving
but no they are not impossible, in fact their difficulty gives many people a sense of accomplishment (something the raids do not).
I beg to differ. While the enrage timers may be a bit rough, that is what makes them challenging. I have no problem with somewhat short enrage timers. They are not undoable if my group can finish a hard mode instance with still most blue gear and some purple armorings from Ilum.