There used to be a column called "Sheets (Owned)" on the user report. This data was extremely helpful for managing users and memberships. Unfortunately, it has since been removed an replaced with "Sheets (Created)". This datapoint is not as valuable because users can transfer their created content to other users.
Please add "Sheets (Owned)" OR better yet "Assets Owned" to the Seat Type report or, as a second choice, back to the User report.