I like running PuGs because it's a craps-shoot what you get in terms of quality. While irritating, I find it a lot better at honing my skills than guild runs, because guildies play smart.
I will mention a couple of things:
The second boss sends out his flares every 15% life, not time-based. Running heroic with some Illidan-geared friends we found that pulling back on damage made things easier, rather than the instinct to race the incoming damage. That way the dots from the flares stay under control. It's still a fast fight, and you need to pick it up once overloads start.
The third boss, the priestess is no stronger than the others, despite being the technical "boss" of the group. Threat of individual guys depends on who you have to face them, but the shaman, rogue, fury warrior and engineer are particularly rough if left unchecked. Note that the engineer and hunter are demons, and can be banished as such. The rest are humanoids. Vulnerable to all CC except MC (and priestess cannot be sheeped/sapped).
As for Kael, I've found the best way to handle the phoenix is full focus. Don't kite it, kill it quick and the egg. He only fireballs unless interrupted, so some FR might be good (as I was reminded on heroic though, too much FR on the tank really cuts into threat since there's no other damage). Arcane Resist, similarly, can be useful. It doesn't seem to affect the lapse dot, but a brush with an orb is resistable in part or in full. Be sure to heal yourself if you can, the healer's got his hands full. Avoid orbs first, dps second.