There are bits and pieces scattered throughout the books about magi who believe that the original Realm, or Eden, was the Magic Realm. That got me to thinking of how that could have come about.
Eden, the original Realm, was the Magic Realm with any Empyreal (Dominion) Eden forming later.
The Faerie Realm formed when powerful beings of the Magic Realm started to interact directly with the mundane realm, with humans specifically. The Dominion formed when a Demiurge of Magic, probably a Kosmokrator-level Spirit, decided to interact directly with the mundane realm and each successive Demiurge of Magic ever since has slowly sapped the vitality of the Magic Realm, which is why ancient rituals like those that give The Gift have ceased to work. The Infernal Realm formed when Faeries actively opposed the Demiurges of Magic.
This is why in most Dominion Lore, the end of days comes about during a reckoning which puts the entire cosmos under the rule of the Dominion, e.g. the Second Coming will involve a new Demiurge of Magic that will convert all the other Realms into the Dominion.