> I also avoid it because I'm concerned about being over-reliant on google (what if they close my account?)

Most if the "sign-in with google" accounts I have seen treat it as a shortcut to creating and logging in with an account with the primary email address of the Google account. So you can hit "reset password" and get a conventional password log-in to an account you previously made with the Google auth. If you get locked out of google, it's NBD.

Of course, this is probably not universally the case.