Best way to think about it as a single universe that everyone plays within. This universe is accessed by jumping between all the different worlds. (These worlds happen to run on individual servers.) It is definitely a single MMO.
So it is one huge world that everyone shares *and* a connected world that people can blip in and out of.
We’ve distributed the servers around our playing community – so that all players can have a decent experience. However, you can connect to any server – and surprisingly the performance is decent.