Client certificates have been a thing for years. They haven't caught on because the user experience is so terrible. ENS seems like client certificates with extra steps.
But, it is definitely a real use-case, so hats off to people for having a go at it!
If you want to trade easy of use against trust and security, you can use a browser extension like MetaMask that can hold your private key (or one of your private keys which you’ve chosen for this purpose) and perform the auth flow on sites that support this stuff. The UX is pretty smooth.
If you want more control, you can build one of these browsers or extensions from source and audit the code yourself. So you can choose your level of challenge/paranoia.
But, it is definitely a real use-case, so hats off to people for having a go at it!