Hey @twang
For this one, you might want to check out Account Level reporting. This enables you to instrument a set of group properties on a user level so that you can do org level analysis as your use case suggests.
If you aren’t sending any group properties, then there isn’t any direct way to using a user property to do the grouping on the UI.
AFAIK, the Create a Group property option will be helpful only when you are planning to ingest group properties.
Let me know if I have interpreted your use case correctly. Hope this helps.