In addition, if you will try to find security of entry points of following path
General Journal >> Setup >> Organization >> ...
it would not restrict access to Customized dimensions, because those still can created from following path
General Journal >> Setup >> Financial Dimensions
If you will go through white paper of XDS, you would find almost same scenario, as a demonstration, where data is being secured using department or Business Unit.
Having XDS with temp tables such as MyDepartments,MYBusinessUnit etc. is more easy to control.