> Whatsapp desktop/web is terribly slow and requires your cellphone to be on at all times.

They have a rather sound reason for the cellphone requirement, though. It's because the messages are stored only there and the desktop/web application is just a gateway to your phone.

https://faq.whatsapp.com/en/web/28080002

This seems like a more secure way to do it than what the others do, which is to store the messages in their servers.