I am working on SP2013 on-premise standard edition. By login as a site collection admin, I goto Term Store Management page (/sites/ABC/_layouts/15/termstoremanager.aspx), then create a termset group and create some termsets. I have NOT assign anyone as Group Manager or Contributor or anything.
Then I create several subsites under the site collection and broke the inheritance. In each subsite I grant userA, userB, userC, etc into the Owner group. So that each subsite's owner are different.
The bad part is, I tested every subsite owner ( userA, userB, userC, etc ) can now open the term store management (i.e. /sites/ABC/subsite/_layouts/15/termstoremanager.aspx). All the subsite owners have almost full control of termset group under same site collection. He can add new terms, modify and delete termsets, etc.
If userA add a new managed metadata type column in one of document library, a new termset is created. The bad thing is userB, userC, userD etc all can modify this termset.
If I remove userA from the Owner group, userA cannot change the terms anymore.
I was planning to create 50 subsites. Each of them will have its individual term set. It seems I have no way to restrict termsetA be managed by ownerA only?