Wild Imps and one or two other guardians on other toons (I forget which) have caused me to get MC'd though.
Obviously the boss has more HP, but that isn't relevant to what we were talking about.
BM with spirit bond standing behind a statue just spamming kill command will kill him in short order. Step out for a mend pet in between mind controls if needed. Any spec can do the fight with ease.
1. Pull the first one (slow guy) out to the entrance of the instance (or rather just run there and wait for him to show up - but don't get knocked out of the instance).
2. Stand there and wait for second guy to reach the entrance (It's okay to plop them both here as the first guy is much slower).
3. Once he's dead, run up towards Kael's room. You'll meet the mage chick about halfway there, so kill her when you run into her.
4. Run with the engineer up near Kael's room. Get him low if you want, but don't finish him off until your remote toy debuff is without 15 seconds or so of fallling off.
After doing it this way, when they rez after you've killed the weapons, you can just kill them one at a time, as they'll be spread out. Even at level 85 in a survival self-healing spec (on my warlock) I had the dps to only face one at a time and I could handle that, so as a 90 you should have no problems surviving even if you can't immune their CC's.
Really isn't any need to pull them all over the instance. Simplest is to clump up the 3 melee guys behind the boss, and pull the caster to the entrance of the room.
That way you can easily start on killing her at start of p3 while the other 3 waste time running over to you.
I used to solo the fight every week with 5-7 chars this way, different classes/specs, I even solo'd the fight with lvl 85 disc priest (twinked with 415 gear + 442 weapon) multiple times doing just that. Funnily, it was my 85 priest who got the drop... just like with Karazhan mount <.<
And as mentioned before, for p4+5, you can easily just put your pet on stay+passive behind the right statue out of line of sight & stand on the other side of it & pew boss to death, Spirit Bond is all you need to stay alive.
https://www.youtube.com/watch?v=y6we4wO48h4 simple video here .. I am still in the process of getting the ashes . So each week still killing him. Also after phase 2 of kael fight starts were he runs back to the room and shatters the ceiling you can summon pet at that point. having potion and warlock candy helps for heals before then. The video involves running out of the room before it locks then running back toward entrance of tk. Spacing out the generals as you kill them .