you’re the only one with your SSL keys. As part of authentication, you are identified. All the information about your device is transmitted. Then you stop identifying yourself in future messages, but your SSL keys tie your messages together. They are discarded once the message is decrypted by the server, so your messages should in theory be anonymised in the case of a leak to a third party. That seems to be what sealed sender is designed for, but it isn’t what I’m concerned about.
Why do you think that Signal uses SSL client keys or that it transmits unique information about your device? Do you have a source for that or is it just an assumption?
Clearly they’re cosplaying as a Canonical engineer whose internal explanation and pleas for them to not take this approach fell upon deaf ears /j