I find the truth is almost the opposite. The REST API is pretty good, at least compared to anything the OGC has put out. While ESRI's tools are okay for authoring maps, their server software is some of the worst crap I've ever had to work with. It's slow, and buggy. And slow. Map tile generation takes 7000 longer than on open source software, on the same hardware.
While technically all their stuff is documented, they have a nasty habit of creating a new documentation portal for every major release. And Google always takes me to the version from three releases back.
Rather than standardization, I just want a way to take a map document and turn out cartocss, or mapnik styles.