Hi @karen,
Great idea to not include a category on import! I’m happy to share that with the team, though I would recommend opening a feature request as well so that other can add their votes for it.
As you correctly note, there is no way to suppress the category on import– at least for events imported from one WordPress site to another. That appears to be the only source where events import the category along with the event. All other sources leave the category alone.
One thing you might try is to create a placeholder category. You can call this something like Uncategorized and automatically assign all imported events into that category. Then, you can bulk edit all events in that category to remove the category from those events, or simply delete the category altogether, which will also remove the category from all the events and leave them unassigned. I know that’s not a perfect solution, but it would be easier than having to manage multiple imported categories.
Cheers,
Geoff