Most people I chat with on Signal uses desktop too, I’ve never heard complaints. Most of my contacts use it now. There were hiccups in the earlier months but now it’s smooth and works great.
I use Telegram every now and then. It’s has some nice features. But it’s not secure. The reason the messages “sync” fast there… is because it’s all plain text and on the server. For everyone to read. This is an undisputable fact about Telegram. The nature of the large channels you mentioned requires this insecure mode of storing chat histories, so that everyone can access. Where as with Signal, everything is E2EE. Except a tiny bit of metadata. Telegram everything is unencrypted until you use secret chats. Again. Different threat models. You can’t really compare it to Signal. It’s more akin to FB messenger. Which is not secure. Or private.
Messages being deleted for everyone is a pretty common feature across all the platforms now. I’m not sure what you’re getting at. Arguably, chat history being stored plain text is much more a privacy nightmare (it’s literally the reason people want E2EE) than anything else.