The fact that if you don't use a burner your friends can share your contact with other apps it's not a signal problem, it can happen even if you don't use any msg app. If you are a real target of a 3 letter agency, very few apps can help you imo. I use signal bc it does what I want, it does not collect your data or shares with others and it works well, it's magnitudes better than whatsapp in privacy and app experience imo. I just use it as a better privacy option to replace whatsapp, not as a secret chat app to escape 3 letter agencies.
Discussion
I must respectfully disagree. It is partially a Signal problem as they require a phone number. Without that requirement, this wouldn't be an issue. There's no legitimate reason a phone number should be required.
Yes there is, requiring a phone number ensures a single person can't add thousands upon thousands of accounts, because access to unique phone numbers is limited.
It's spam prevention.