Remember Onyxia and Thrall: they can be at two places at the same time... for us. You should be aware that lore-wise the Kael'thas from The Eye is chronologically prior to the one in Magister Terrace, like the Onyxia in SW is prior to the one in her lair.

As far as the "being in two places at once" thing goes, it does make sense when we consider Onyxia and Thrall.

It's still weird to me, though, that two different versions of the same person exist at once. With Onyxia, she's in her human form in Stormwind and she drops that guise in her lair, but it's still supposed to be the same person (or dragon) in both places. Yes, the Stormwind version is chronologically prior, but only slightly. With Kael'thas, though, he's a very powerful 25-man raid boss in one instance, and a regular 5-man boss in another. It becomes hard to believe that he's supposed to be the same person existing in the same time period.

It may be true that the Magister's Terrace version is supposed to be chronologically prior to the Tempest Keep version, but this isn't a simple case of "he was over there before, now he's traveled here" like Onyxia and Thrall. The large difference in his strength indicates that a pretty significant amount of time has passed.

Maybe I'm thinking about this too much, but inconsistencies like this bother me.

I know exactly what's going on here. We killed Kael in the Eye as a 25 man boss, and he's back as a 5 man boss. Just like when players die, and come back a lot weaker.

That's right-- Kael is rez sick. He should have just run back.

Well, once you defeat Kael in the Eye, there is a small event when you turn in the quest at Shattrath where he announces he's not yet dead, and he plans bigger things. And his new model is him near death, with a crystal through his chest, like his life-support. So he is a lot weaker yet, he's not really doing much other than overseeing his operations, hence why he's just a 6-man boss, and not down there in the 25-man.

You're seeing it wrong cpsethgt, the 5 man kael is the one AFTER the 25 man one. He's been severely weakened, this version is just a mere (mind the pun) skeletal form of his former self.

After being hit by legendary stuff I'm surprised he's still alive.

So yeah, chonologically 5 man Kael is after the 25 man one.

What your missing in this 'chronology' is the attunement process. Your doing the quests/attunement your in your own timeline and when doing that instance your sharing that with the other players.

This gets pretty stupid when they remove attunement (though if they keep the quests thats fine)