Demetrios1453
Legend
Two points here - in the Eberron PDF, the setting being part of the standard D&D Multiverse is only one of several options available, and it's specifically left for the DM to decide. So, officially, Eberron being part of the standard Multiverse is a definitive "maybe, it depends."I personally am not at all a fan of this idea that there is explicitly one true cosmology (the 5E Great Wheel) that all campaign settings share. Even 4E allowed Eberron to have its own unique cosmology rather than force it into following the World Axis model. If I understand correctly, in 5E Eberron the true cosmology is the Great Wheel, and Eberron's unique planes of existence are part of some kind of inferior sub-cosmology contained within one Crystal Sphere.
I similarly dislike the idea that all worlds share the same Feywild and Shadowfell (although to be fair this detail popped-up late in 4E).
Mordenkainen's Tome of Foes also says that all elves in all worlds of the Multiverse were created by Corellon, even if a given world's elves no longer remember their creator. Basically, any campaign setting whose origin for elves does not involve Corellon is now non-canon. It's not too much of a stretch to say that the Forgotten Realms' cosmology in 5E is now the cosmology of all D&D campaign settings, and any source that contradicts it is unaware of the true nature of the Multiverse.
Secondly, as already pointed out, the current standard D&D cosmology is actually Greyhawk in origin, with the Forgotten Realms only adopting it afterwards. In fact, a unique FR cosmology was attempted during 3e (the "World Tree" cosmology), and it's quite different than the standard Great Wheel Multiverse. It was also widely disliked and quietly dropped for a return to the standard moddel afterwards...