WhatsApp and Facebook Messenger offer the same level of security as Telegram. In fact, I think WhastApp is more secure since it does E2E encryption by default.
It's true that Telegram is about "fun" and not security. I just wasn't sure if you tried to imply Telegram is like Signal with a focus on fun as well, or you just meant most people don't care about security and would rather have fun chats?
(I am not here to defend Telegram's portrayal of itself as a secure messaging service — Telegram is grotesquely bad on that axis)
tg is light on resources like phone storage and bandwidth (and hence money) and has excellent multidevice support.
apart from that i don't belive one can have a seriously private conversation involving a device running popular versions of android/ios.
If you look only at encryption, WhatsApp is even better.
Once you factor in the fact that all your metadata is vacuumed into Facebooks data lake and that it might very well end up in Google Cloud if either you or someone you chat with activate cloud backups.
WhatsApp, for all its faults is E2E-encrypted by default and all the time.
Not that it helps much unless you avoid activating backups and convince all your contacts to avoid backups.
I don't like WhatsApp (anymore), but we should stick to the facts.