Its too bad you didn't bother to actually, err, use (?) Telegram before writing about it. There are two modes, and you conflated them together. The centralized messaging, which allows groups, is NOT end to end... its end to server encrypted. Telegram ALSO has End to End encrypted, its called "secret", where the is no central server. Secret mode has a number of privacy features, like exploding messages, and such. You can either both or either.