No, thats exactly it. When you post something on reddit, Google collects your browser information for your "unique identifying number" by having scripts implemented into Reddits site. Google then knows, that u/Prethoryn is your account and they can then collect the data from your reddit account and link it to you.

But your Lemmy instance (so far) does not do that. You post something here and google sees that some "Prethoryn@lemmy.world" guy wrote something, but their data-collecting can't link it to your unique identifying number, because lemmy.world does not collect that information from you. And of course, your comment is federated to thousands of other instances. But they also can't sell more information than what is available when you look at Google. If lemmy.world decides to implement tracking, this of course changes. But for now, your comment is not linked to you and it's definitely a step up in privacy (regarding companies) than before.

The other aspect of privacy, personal privacy, is of course not so good on the fediverse and that's where your points make valid sense. If you want to delete your comments because your friends discovered your secret account, it's basically impossible because of the federation.