Yea pretty much 3 are rollface (Well Millhouse is if you have enough dps), disruptron is such a pain, but with some practice it's doable (at least as a ranged). I'm Ele Sham (H) 520 ilvl and I used following tact : start easy on right side of the arena, jump over right beam, then over back beam, then beam that doesn't touch wall comes (it's my reference point). Keep dpsing until this very beam goes and comes again, then pop 1 CD (for me that would be Primal fire elemental), repeat until it comes back again (boss is about 45% now) pop all shit you have and pray you will survive those 15 s. I guess each class can time it accordingly, but routine is key, always make same moves (same side of the room) so you have time reference, you can learn how to react each second. Then the only variable is ball flying around. GL
Killed Disruptron as a boomchicken after hundreds and hundreds attempts. All 3 others are easy, a good raider can achieve them easily.
But for Disruptron I had bad RNG's and lag issue that made it very difficult for me to jump over those lasers.
Well, as the people above wrote... Zen'shar, Millhouse and Epicus are fairly easy compared to Disruptron where you need tons of practice and quite good dps too. If you are melee... you are gonna have a bad time.