There's end-to-end encryption. It's fine that you can chose what needs to be private, and what doesn't need to be.
There could be several reasons as to why the servers are not OS. Why do you need that part to be OS? Seriously, why?
Oh, so your problem with Telegram is, that it had some issues in the past, just like EVERY other app in the beginning? Nice one. :-)
So, let's summarize.
- You lie, and say that there's no end-to-end encryption when there is.
- It would be preferable to have OS servers, but it's not a major issue, since everything else is.
- You have an issue with something in "Back to the Future"... Which is no longer an issue.