Difficult to use? I'm even more confused as there is literally nothing to do to "add" someone.
As I stated our entire family uses Signal across Android, IOS and desktop. That age range in our entire family group is 20s to 70s and I happen to be the only user who would be considered tech savvy.
Contact permission is only required to associate a name with a number. All you would need to do is type in a phone number and Signal would have worked.
I agree that it would be nice to have another root artifact for using signal (screen name, email, etc). The one frustrating piece about Signal is not being able to use it across mobile devices.
However it needs to be considered Signal was originally securing texts via TextSecure. It didn't, fundamentally, come up as a Slack or Telegram competitor. So that design decision may make it feel "behind" in comparison. However, I'll again state that I don't trust the others. There's no way you could force me to use FB Messenger or Google (product here). Most complaints here are fundamentally still UI/UX, not privacy. And useable privacy was the original intent. Signal has that in spades.
As I stated our entire family uses Signal across Android, IOS and desktop. That age range in our entire family group is 20s to 70s and I happen to be the only user who would be considered tech savvy.