When Telegram first launched, people were reading their crypto whitepaper and going "Whoa, this is weird. You should probably not be doing it like this", and the reply was "Well, our 6 world champion coders (did you win a coding world championship?) think it is nice. Deal with it".
They then launched a bullshit crypto challenge (which would have been secure even using crypto primitives we _know_ are insecure). People told them that wasn't how it was done. They replied something cocky about world champion coders.
A couple of months later, someone found an gaping hole where the server could MITM every newly started secret chat (which their hack for forward secrecy a couple of years later would have made possible for every 100 messages).
I think their attitude towards encrypted messaging hasn't left puberty yet, and I recommend against it for everyone looking for a secure messenger. For anyone looking for a more convenient whatsapp without caring much for privacy by default, I don't mind recommending Telegram.
Regarding your future threat model: I certainly can't say whether having a copy of a significant chunk of my private communication on a server in Russia is a future threat to me. On the other hand, I don't use any social media, and have proper data retention policies on most of my online communications.
To be fair, Telegram doesn't have servers in Russia.
I've found Telegram to be more than good enough for day to day communications where I would previously have used email or SMS/MMS.
I'm normally on the Signal side of this argument, Telegram is trash and should not be used, but basic features like message editing are legitimate requests. I use Signal heavily and a number of times a day at least I or someone I'm chatting with corrects a previous poorly phrased or incorrectly typed messages. Because Signal has no mechanism for that, it usually involves retyping most of the message or the relevant word and adding an asterisk. I believe if Signal had built-in message editing support it would be used far more than I currently see corrections.
To be clear, I would expect Signal to allow me to see previous versions of a message and clearly indicate that it's been changed, but message editing is a valid feature that Signal should absolutely implement.
Further, the goal of Signal is not to work well for people who are accustomed to the various quirks of text-based communications that have existed since forever, but to provide a secure, modern communication client that normies don't find difficult to use. Message editing has become a standard feature of any usable modern messaging client.
Until then, throwing the "homegrown encryption" argument to argue for Telegram's weakness is hand-waving and a straw man.
Telegram's security is sufficient for the threat model I have to face against now and in the future.
[0]: https://security.stackexchange.com/questions/49782/is-telegr...