Facebook actually has had optional E2EE with the Signal protocol since at least 2016 (in my experience), as "secret chats". This puts it on a better security standing than Telegram.
Yes, but Facebook (and others) uses the Signal protocol in its optional E2EE chats, because it has withstood the test of time. But Telegram uses its custom protocol (MTProto2) in its optional E2EE chats, which has a host of problems and has not withstood the same weathering.