It seems you will have to convince with actual reports and output that the applied settings are indeed covered in the GPOs and as per the requirement, process should be to apply the GPOs to a test device and a test user and carry out the testing of each settings such as Screen Saver, Deskto Background, Password Policies etc.
With test user account you can extract the User GPOs - gpresult /r /scope:user
On the Test device you can extract the Device GPOs - gpresult /r /scope:computer
GPResult utility can generate an HTML report on the applied resulting policies, this report will contain detailed information about all system settings that are set by Group Policies - gpresult /h c:\reports.html
For specific account or test account - gpresult /r /user:domain\username
Combine all the reports and you should be able to present the actual settings applied and from the GPO Console export the policy reports this should be sufficient.
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.