Its actually the same thing. A shared identifier. Of course email is another thing to separate for separate identities. But it is way more widely known that email adresses are used ad an unique identifier.
If you agree that said platforms leak lots of other identifiable data (which you seam to) then thus it is a fair statement to say GitHub hiding public keys do little to enhance your privacy. And thus one can reasonably conclude that privacy argument doesn’t really hold with regards to SSH keys.
I’m happy to agree that it’s bad UX and probably should be advertised better so people are aware they should follow the (in my opinion best practice) of using a unique SSH key for GitHub.
The whole intention was to raise attention to a less often mentioned part of the information github exposes about accounts.