Default Versioning Settings - Number of Versions to retain

Facing exactly the same challenge. Users have been encouraged to use OneDrive instead of their local My Documents location, which resulted in large number of users migrating their PST and OST files to OneDrive for Business. Given Outlook constantly updates PST files their OneDrive storage is quickly being consumed by the multiple versions of the PST files. The suggested way of restricting the versions via the user interface is not relevant as it sets version settings for a specific user, not tenant wide. There is a setting now to block files in OneDrive for Business based on extension (OneDrive Admin center), but obviously there is a need to clean up files that are already there. PowerShell is the way. What a mess.