Nowadays, a majority of apps require you to sign up with your email or even worse your phone number. If you have a phone number attached to your name, meaning you went to a cell service/phone provider, and you gave them your ID, then no matter what app you use, no matter how private it says it is, it is not private. There is NO exception to this. Your identity is instantly tied to that account.
Signal is not private. I recommend Simplex or another peer to peer onion messaging app. They don’t require email or phone number. So as long as you protect your IP you are anonymous
You literally don’t understand how hashing works, got it. Please educate yourself on this topic. In short, “connecting your existing contacts” is ENTIRELY possible with hashed phone numbers; it’s not even complicated or tricky. To claim otherwise, as you just did, is nothing but trumpeting your own ignorance.
As for deleting (and propagating deletion of) messages, this is most definitely NOT a matter of “just trust us”. The client is open-source! We KNOW how it works. We KNOW that deletion propagates across devices when you tell it to. We KNOW that the service cannot see your unencrypted messages, and that the encrypted messages are made with AES so even quantum computers in the future can’t decrypt them. This is incredibly far from “just trust us”.