Collections created by other users in Workspaces cannot can accessed, edited or permissions changed without requesting access to the Collection Owner, even as an Admin of that Workspace.
As an Admin for the Team (and/or Workspace) it is expected that the Admin has full CRUD rights over that Workspace and any Collections within that workspace.
The problem we now have is orphaned Collections after moving to a new domain. Some of the collections we use were under old email addresses that are no longer valid and therefore that user can no longer get in and change permissions. So these collections cannot be deleted/accessed/changed/moved.
Give Team and Workspace Admins full CRUD capabilities over all objects (but in particular Collections) within the Workspace they have Admin rights for.
RBAC should flow down from Team → Workspace → Collection.