> Also if they ever get locked out from their oauth account they can use the email to create a password and login via the normal way.
This is exactly my point ! You can't recover your account if you don't know the mail used for registration. Even if you remembered it, no check could be made if Apple stopped to proxy the mails for one or another reason.
With other providers, you could always recover an account because your email address would let you prove the ownership of the account.
You can look up any private relay email address you've had provisioned in iCloud settings. It shows what service it was used or and the email, also allowing you to disable the address. This is also available from the Apple ID manager:
Is that not the same with if Google block my account? I won't be even able to login to my email for simple password reset or to verify I'm the actual owner of the email.
This is the problem with one click account vs email entering. It is a risk users should be made aware of but it is still their choice. And for some critical services I'll use my email, for other like the app in question, or most apps on the App Store I'll use one-click install, also most of the time there is no need for me to have an account. Most data can be stored on device without the need for user authentication.
This is exactly my point ! You can't recover your account if you don't know the mail used for registration. Even if you remembered it, no check could be made if Apple stopped to proxy the mails for one or another reason.
With other providers, you could always recover an account because your email address would let you prove the ownership of the account.