Hi Danie
Downside of the authorization based approach is that these authorizations are also relevant for the MDGM UI. Therefore, revoking certain autorizations will have an impact on the MDGM UI for that user. Of course, this is only an issue if the same user uses MM0x and MDGM.
MDGM governs fields, not maintenance status/views (as one field can be assigned to many maintenance statuses).
To set fields to read-only for the backend transactions (like MM01, MM02), please check IMG activity Logistics - General -> Material Master -> Configuring the Material Master.
Best regards, Ingo