Transport encryption is table stakes. It's really no longer something that can be mentioned as if it were something special. When I browse to a random website I don't think “wow HTTPS, so secure”. The channel client <-> service is encrypted, but the service still gets all of the data in plaintext.
On a technical level, Telegram is are as secure as Facebook Messenger. Both offer transport encryption and optionally E2EE secret chats. Actually, I might trust Facebook more (on a technical level) because they don't have Telegram's disastrous history with home-brewed crypto protocols.