I don't know about planescape in general. But it seems that many, if not most, of the elements tied to it are special. They existed altered but unbroken in DnD for many years. They were then tossed out to make way for "good lore" in 4e. So, yes they have a special place. You haven't yet shown me a well reasoned argument of why 4e's cosmology has a special status.
As already pointed out: "Good" is highly subjective. Also, every edition, I would assume, tried to make their lore good. I fail to see how 4e was the exception here. If anything 4e was the one that threw out existing lore and therefore made it less good for long standing customers. Decidedly un-good in that sense.
I don't think that they were talking about sheer words, or whatever metrics you claim we are using, though I don't know for certain I am not in their head. My metric is how much of existing elements still remain. How many times I would have to STOP using my existing game/cosmology and start using 4e. And how many elements were retconned or wildly changed for no good or apparent reason. Eladrin as grey elves, Tieflings as human-devil pact makers. Dragonborn (with or without mammary glands). Okay, onto now chapter two..
Either way, I'm not seeing you answer the question. What did they ADD? They simplified but what did they add? What made it good lore as opposed to different lore?
Um... aren't you who said...
... from later down? I thought you were.
You don't want to have to run someone else's game.. err.. endevour.. but you have no problem if all the races and classes are directly tied to a random cosmology involving the gods, primordials, etc. Interesting. Double-standard much? Yes there is no longer a law-chaos conflict, except there is, but that is all that you now no longer have. Instead all the races are directly tied to specific gods and the history of the world. That is fine if you prefer it. If not you suddenly have a whole bunch of gods that likely to not exist in people's homebrew settings being inextricably linked to the core races. Again, seems like "someone else's endevour" is much more heavily involved here.
Unlike the elemental chaos, astral homes and god-primordial conflict, that was entirely different?
If I remember the blood war correctly, and I mean the real blood war, then this is basically the "early days" of it. But beyond that, nothing here is better it is merely different. It is no more or less an incentive to participate. The players are no more or less involved.
All editions tried. Some thought the best idea was minimal involvement. Others (looking at 4e) tied it into everything. 4e just decided the great wheel was too silly and threw away a metric tonne of lore that had been represented for decades and decided a undescriptive but oddly super-involved cosmology of bland gods vs. over the top evil gods was a better fit. I agree with others.. that's disney-esque. It represents everything wrong when people say L = G and C = E, taken to extremes and then said to be better.
Yes, 4th Ed really beat you over the head with the whole Primordials (Titans) vs. The Gods deal (The Dawn War), and that Tharizdun dude.