In reply to mark k..
This just isn’t true:

Then REST API. 6 months after it was officially merged in core there is still no place it is used in core itself, and you will find very little usage in a wild.

It’s used by several popular plugins already including one of my favorites (Formidable Pro). The inclusion of the REST API is one of the main reasons I’m sticking with WP.

I agree with the rest of your points though.