The reason the messages “sync” fast there… is because it’s all plain text and on the server.
Yes, I'm aware but it comes down to having something that really sync well 100% of the time, very quickly and without having to constantly dealing with errors such as this https://twitter.com/signalapp/status/1350631024351346689 or "signal can't display this message".
Messages being deleted for everyone is a pretty common feature across all the platforms now. I’m not sure what you’re getting at.
I'm getting at the fact that most platforms do stupid shit like "this message might not be deleted if the receiver already saw it" like WhatsApp does and/or replacing messages with placeholders saying "this message was deleted". Telegram can be plain-text and can have a lot of issues but it guarantees that stuff is actually removed without trying to bullshit you like other do.
Eventually Signal might be funded by the US/CIA so who says it is as secure as they advertise it? If we assume that your privacy / security is broken (because it is) I might as well use the platform that provides the best desktop and mobile experience with fast syncs, ability to disable animations, have real desktop apps and not electron shit.