Facebook's Messenger app is TLS-encrypted (i.e. encryption happens between client and server) unless special E2EE mode with Signal protocol is enabled.
Telegram is encrypted with client-server MTProto (i.e. encryption ALSO happens between client and server) unless their the special secret chat with its hand-rolled E2EE is enabled.
In LTE networks SMS uses the SNOW3G[1] encryption between the cell-tower and phone. This is also equivalent to client-server encryption in that the server-side area covers the more or less TelCo side decentralized SS7 backbone where message travel more or less unencrypted.
So by default with all three Telegram, Facebook, and SMS, all messages are readable by the vendor. Telegram and Facebook offer E2EE as an opt-in measure, but given that neither offers it for groups, they're not a viable option. Signal uses E2EE for everything, hence it's the recommendation by every security expert out there, nobody's recommending Telegram or Facebook.
There's nothing puristic about expecting companies in 2020 to implement basic security like E2EE for everything, by default. After all, we're not talking about anything short from protecting universal human right to privacy here.
Telegram is no worse (or even might be better) than email, your banking website, facebook, your credit card, etc...
It's 100% better than SMS though, which is completely unencrypted.
I'd bet that for most people its an upgrade in security and privacy.