They have a list of what websites i sign into with my Apple ID. Which is more information than they used to have. If you switch from signing in with your email address to signing in with your apple ID, that's one more entity that knows about that relationship than otherwise would.

I'm not trying to say this is a bad thing, I love what apple's doing here. I'm just trying to push back against any suggestions that apple is giving something up. They are collecting more data about their users now than they were previously, and positioning themselves as the gatekeeper of user identity. There's every indication that they're doing this for the right reasons, and it's good for users, but it still increases their control and their stored user data.