For Disruptron the DPS requirement to meet his 104 second enrage is 100.7k, for a shadow priest, that number is a phenomenon, but next to impossible if you actually do the fight without levitate and the safe spot.
Epicus has a slightly more forgiving enrage of 110 seconds, which only requires 95.2k DPS, but you lose 15 seconds of pre-pot to role-play, this would be possible with near BiS gear and some decent luck.
Millhouse was tight if you got bad starting spawns for the crystals, but once you get an attempt where you can block both of the crystals for the first 1-2 sets, the enrage is easily met.
The eye beam guy was easy, but for classes without a strong and consistent AoE attack, it's going to be rough with the amount of time spend on the adds.
I personally love how hard it is to kill these guys, what i don't love is watching a fire mage 20 ilvl's below me wiggle in and roflstomp millhouse without even batting an eye, simply because he is blessed with heroism.
If any sort of balance is to be maintained between classes on the difficulty of meeting the enrage timer, you can't allow 3 classes to use a 10 minute cooldown in a 2 minute fight.
EDIT - I have been enlightened as to the mechanics of Disruptron's "teleport enrage", i assumed it was based from fight start, but it is in-fact from ~35%, meaning the fight has two DPS checks, one from 100% to 35% which requires a mere 64.8k DPS, and a 22-24 second burn from 35% to 0% which demands 152-166k DPS (I feel this is obtainable, but i guess I'll see)