With Signal, if a the numbers registers a new account like in this attack scenario, 1. the attacker cannot access old/pending messages (as they are always encrypted), and 2. the person on the other side of the conversation gets a warning that the keys have changed, thus need new verification before continuing the conversation. So, Signal is more secure on that front.

Telegram got two factor support which a user can enable anytime for security.

Also, there's a PIN code you can use to protect from transferring your number to another device. This is periodically asked by the client app so that you'll remember it.

Yes

Yes. But you don't get message history.

I thought that you can get message history but it is not automatic.