You're missing the original point. rgbrenner is talking about auth solutions like Auth0 where users can use username + password to sign up/login, and when you eventually are gonna have to leave (which, if your business is successful, you eventually will), you'll need to reset passwords one way or another.

Of course, if you only use third-party authentication for your service, it doesn't really matter what's in-between there, you can work around it.

what's more likely - you being able to talk to Facebook, Google, or Apple to let your app/site use their authorization solution once their algorithm has decided to ban you, or you fixing your bug.

That they will ban you for one reason or other has a very high possibility of occurring before you go out of business.