Unfortunately, some Telegram usability comes from a reduction in security. Things like seamlessly going, with full chat-history, between multiple devices is a bit tricky when your protocol only permits one person to receive a message once, rather than storing the messages unencrypted on the server like Telegram does.

One "secure" approach would be that of the older Skype clients, where chat history synced between the logged in clients of a user. However, that was a horrible user experience, made worse by bad notification management.

So while Signal can get better, you will probably always have to decide between usability and security, which is most likely the very reason that "normal" people always end up with the less secure solution, which in turn renders the secure solution even less usable with its smaller userbase.