portal.get_org_users does return a list of users with a list of dictionaries. But, yes the groups part doesn't appear to work.
But what you can do is then use this list to recover each username, then loop through these with portal.get_user("username"), then recover the "groups" key from that.
Portalpy gets some getting your head around, often shuffling between the name of something or its id.
But it is very powerful.