True they'd know which sites you've signed up to, but not the login times, unless the service emails you every time you log in.
Every time you sign into an app, you get redirected to the auth provider to open a session there. So of course they know your login times.
I don't think you followed the thread. I began discussing the OAuth privacy nightmare, then the counter point was that the with email auth providers know anyway, but they don't know the login times necessarily, unlike with OAuth.
Three main providers
(Apple login is in nearly every iOS app and most websites)