You are clearly not the target audience for Signal. There of course is a space for the type of app you're describing, but saying that the tradeoff that Signal has chosen was a mistake is to misunderstand the goal there.
Do you have evidence that this is happening? Otherwise, completely FUD.
The goal I was referring to is making it easy for regular folks to use end-to-end encryption. Any real measure of security needs to be practically usable by the intended audience, and the clear and consistent intended audience for Signal is regular folks who don't have a sophisticated threat model. If any other identity scheme were used, I'd guess the number of Signal users would be an order of magnitude smaller.
This is not to say that there aren't great reasons to have more elaborate secure messaging systems that address these questions, for anyone with a different security model.