I think the way you think of Orcs is not the way that TSR or WOTC has in the past; the planes in the 1E MotP are presented in the same manner as Orcs in the MM..
I think I finally had an epiphany.
Let me see if I can work through this so that it makes sense, because, for me at least, it seems to explain why I'm having such an uphill battle trying to make my point.
The difference here is between a resource and a setting. The Planes (not Planescape, but all the Planes) are a single setting, not a resource.
I don't know what @Hussar had in mind, but perhaps the goal is to present an alternative interpretation of Appendix IV of the PHB? As someone who first learnt about Acheron's cubes and shards in Jeff Grubb's MotP, I thought that it made the eternal battle between orcish and goblin spirit-hordes considerably less compelling, by making their battleground rather silly. (The description of the earthmotes in Asgard/Gladsheim struck me the same way.)
Instead of Hussar's version of Acheron, then, I might want to publish a version that is better suited to the orc-goblin conflict than the canonical version.
And that's probably fair enough. I have to admit, before 4e came out, I would have never, ever, in my wildest imagination, thought that repurposing some esoteric, almost never used critter like an eladrin into something that became one of the most popular races for the game would have caused that much angst.
I'd have to go take a look at the 4e MM, I can't remember what 4e has to say about kobolds, but, I don't recall a link to dragons.
Does this make sense? Is it fair to say that The Planes are a setting and not a resource?
This may be a reflection on my own shortcomings as a gamer, but I can't say that I agree, and I think that's because of my own association of the name 'archon' less with a creature and more with a historical office, and one that I could see used by various creature types. So for me, 'archon' is a generic title. An 'archon' has never existed in my imaginative consciousness as a mythical creature, not like unicorns, angels, demons, or giants have. Celestial archons strike me as a just another subset of angels, though I'm sure some Planescape fan will condescendingly tell me how wrong I am about that. An 'archon' was always an official, a 'lord' or 'ruler' of ancient Athens. So regardless of the past editions, I don't see 'archon' as a creature nor do I see it akin to an octopus being used to apply to both a cephalopod and a flying mammal. Furthermore, that analogy is incredibly silly given how animal names are in fact reapplied to other unrelated animals, both in English and many other languages.That is what we do. But it's a rare thing for monsters of completely different natures to have the same name, would you not agree? Aside from chromatic and metallic dragons (which are still both essentially dragons) I'm not sure I can think of an example. For simplicity's sake it's better that they have different names. Which is what I expect WotC will do if they decide to incorporate both.
It's not even remotely the same. One is a generic title that is expected to apply to different people. Another is a species name. It's more like having the word "octopus" apply both to an aquatic cephalopod and a flying mammal.