Signal just doesn’t feel like it’s iterating fast enough.

Development is always a lot harder when you need to consider all the privacy aspects. When you don't, you can be Telegram and give fancy features real fast.

you can bet there’s a back door in there

I mean you can educate yourself about cryptography and find the "backdoor", the source code is out there for both the server and the client. And I assure you there are a lot of people in academia who would love to do that and get lots of citations, but no one has ever done so, so maybe there is none? That is if we don't consider all the security audit commisioned by Signal itself on its app/server.