I don't understand : in my experience it's still much easier to set up another email account than to deal with authenticator requirements, where you might be forced to use Google's Authenticator ?
The logical answer might be to just not use Sign in with Google but some services don't even let you use username/PW, it's sign in with Google/apple/Github etc.
The sites also shouldn't be 'lost', don't they have a way to register another kind of login from the same one ? And you can always make a new, platform-free account − better do that sooner than later !
Please name and shame the websites (like Advent of Code and Rebble) that only allow a login through platforms. And services that only allow Google Authenticator.