I don’t think it’s a valid argument against metric, just a thought experiment to consider about the time needed to implement. Converting would be a slow process, but I agree it could be an economic boost as swapping things is a largely a manual process
Requiring email of phone numbers isn’t always something virtuous like stopping spam. It’s also often about first party data acquisition. Even if some people use burner accounts, most won’t, and that means more data to share with advertisers.