You can write your own, maybe high-performance, end point for "classical" AJAX requests as well, which is something not really explored and documented anywhere. I doubt that it is the better way, so I would suggest to just let things live that are not yet officially deprecated.
Aside from that, pretty much everything that is suggested by the "official" development side of things, is either proven to be "not the best" on this very side or in GitHub repositories all over the place.
My (slightly personal) opinion on this topic: Let things live aside of each other. We have that many and that different and diverse communities in "our" nano-cosmos named WordPress, so we might be able to accept that legacy stuff has its place as well as new and maybe not-that-bad ideas like the REST API.