It’s about your posture. Most people who use signal use it to have privacy from governments. They’re not hiding that they use signal, they’re hiding what they write on signal. In this case, using your phone number isn’t a big deal.
Some people, have a tighter posture, which could translate to your position. In that case, something like Briar could fit the bill.
Lastly, security and privacy are not the same thing. Google products are secure, but they are not private. Self hosted sftp, for example, is private, but may not be secure. Signal is definitely secure, at least enough for general and governmental use. So, it seems, is telegram. Signal is more private than telegram in many ways, but it is not the gold standard for privacy (because of its use of phone numbers as usernames), but it is “good enough” for the masses. The balance between good for everyone and zero-knowledge private for everyone is delicate, potentially impossible. Honestly, I don’t know if signal was able to strike that balance perfectly, but they did a much better job than many other services, certainly than those others that are accepted by the masses.