iOS Accessibility Settings ~ auto-magically compliant?

I asked a group of accessibility subject matter experts this question but
wanted to extend it to this discussion group. I admit I'm rather hoping
that a note in the WCAG that speaks to this situation might be possible.

   - Does iOS's Accessibility Settings, excuse designers and developers
   from ensuring that the default view is accessible?
   - What is your view on custom components, is it bad that they aren't
   connected to the suite of iOS Accessibility Settings?
   - If a person or organization complains about the accessibility of an
   iOS item that is a native iOS item. Who is at fault? (This one is more of a
   legal question and my brain immediately thought of Winn-Dixie when I was
   added this.)

For example:
Can designers now choose text colors that don't meet contrast requirements?
Is it ok that the native iOS switch is not contrast compliant because iOS
Accessibility Settings has a switch that enables the appearance of a
visible label?

My view is that this situation isn't unlike a website and browser settings.
We don't rely on users adjusting their browser settings to make elements of
the site accessible and so why would it be any different for mobile?

At the moment, I'm asking for custom radio buttons and checkboxes. I was
informed by the iOS mobile dev team that their concern is that custom items
are not associated with Apple's Accessibility Settings. Also if something
were to happen I was asked wouldn't that be more of the fault of Apple for
not having a native radio button or checkbox? Again I keep thinking
Winn-Dixie.

This is a topic that repeatedly resurfaces at the organization I work for.
I do my best to reach out to other accessibility specialists because I
would just be the opinion of 1 at my organization. I think it would be
helpful to have this documented. Especially for folks who are working on
changing the minds of some folks who are new to accessibility.