

The big upside of signal is that it is better then SMS, and has more adoption then any of the other reasonable options. Adoption is still not enough to make it that useful when compared with Messenger and SMS and even with this addressbook thing your complaining about trying to drive it.
Big downsides abound too including needing a phone number, and being tied to a phone.
You can share a name or handle now but I think you still need the phone number otherwise though you no longer have to share it.