Well, nixing Otherness leaves room for that.

Or we could say that Vortex can't be separated from Serenity by more than a certain distance, in order to be sustained.

Hmmm... a thought. It may be that Vortex can act as a conduit for Serenity, which is how she's able to power things, to a limited extent. It's just drawing from Serenity's magic for power, which can then be used to activate power generators or whatever for high power applications