I completely agree that WebSockets are a very good innovation and have their place but I do think that there are a lot of situations where you can achieve the same result easer with SSE and using a HTTP PUT to send messages back to the server.

For example a collaborative project management tool like Asana where saves are silent and update live on other peoples screens is a better place for SSE and a REST api than WebSockets, where as a real time game is probably a good place to the latter.