OAuth sites will let you change your OAuth provider or even better switch to a local account on their site and use a password manager so you don't tie everything to an OAuth provider unless the site will accept a self hosted one.
That includes password databases.
As the other commenter said, there's zero risk giving a dodgy site a randomly generated password used only for that site, the randomly generated password gives them no information or pathway to any other web site.
It's the old twin airplane principal from the hacker's dictionary: the virtue of putting all your eggs in one basket if the basket is built very well.