Fortnite's "creative mode" is a game level loader, not a metaverse. One creator makes a mini-game and uploads it, then others can visit. It's not a shared-world metaverse. Other game level loaders include Sinespace, Breakroom,and Sansar.
Decentraland is in between - each user uploads their own parcel, but it's part of a shared world, where you can see multiple parcels at once.
In a real metaverse, you have neighbors. A very large number of people can each contribute to building a big world. Such systems are very rare.
That's not in line with Disney's business model. "The media giant will work with the Fortnite studio to create new games and an entertainment universe where consumers can “play, watch, shop and engage with content, characters and stories from Disney, Pixar, Marvel, Star Wars, Avatar and more,” Disney said in a press release." Think of this as an expansion pack for the Marvel Overextended Universe.
