No one gets to decide whether or not any worlds are connected to each other, via Planespace or whatever. They already are. In the meta of Dungeons & Dragons, Dark Sun things have appeared elsewhere in other games. Greyhawk things have appeared elsewhere in other games. All the terminology of all the facets of D&D have appeared back and forth across all the settings. It's already happened. It's been written. It's been produced. It's been published. And just because you as a specific DM do not want your specific table to be "connected" to any of it doesn't matter. You are a part of the D&D multiverse because you are playing D&D.
The best you can do is say that for your table and your game and your little pocket of the D&D multiverse, it isn't "connected" to anything else. It is it's own little area where never the twain shall meet. Which is great! Go right ahead! You can SAY whatever you'd like. Every DM's prime material plane for each game they run may or may not have any connections to any other game being run in terms of that DM's narrative. I mean usually there *is* a connection even if you don't mean it to... seeing as how you usually are using the exact same monsters that happen to have the exact same stats as the multitude of every other DM's pocket plane, and you use the exact same magic items that have the exact same names and abilities as the multitude of every other DM's pocket plane, and the physics of your world involve their exact same representation via the exact same game rules as the multitude of every other DM's pocket plane... but sure, yours is it's own thing. You can say whatever you'd like.
But because you are playing D&D, on the meta level you are part of D&D. Whether or not you want to admit it.
