I have raised a support ticket.
It is logical to me how I put it.
Primary WP role overrides a lot of stuff your roles will do.
If the WP roles can be blocked from being changed then your roles have more value.
A standard subscriber (user) (wp role) who I would example like to add a user or change that users password can do that with those role manager permissions listed, as role manager allows to access user settings backend. Allowing minimum access via role manager to user settings and also allows that delegated person able to make anyone a editor, admin or any other WP role. If WP can be blocked from being changed then that would help keep the backed more secure.
Via the email/support ticked I’d consider doing a mini video cast to show you if you can’t replicate it.