I would generally agree with you, if it could allow you to sign-in on multiple devices, and share message history. I understand why it doesn't do either one, but it does cripple the experience
Technically, you can sign in on multiple devices and share history. I share between my phone and multiple desktops. You just can't do it between two mobile devices.
Yeah you can. I have it synced on desktop, phone, laptop. The kicker is that it will only have messages starting from when you synced and log in. If I added a new device, it would not see messages from yesterday, however it will start syncing from all devices from that point on.