In a sense you are correct, but remember that Duplex only works because it is limited to a very strict well specified domain: scheduling for restaraunts and hair salons. That is, Duplex only works because there already is a de facto specification for these transactions. It requires a lot less effort overall to just formally specify this de facto standard and deploy it once and for all, but of course a top down approach rarely works. This actually reminds me of the failure of the industry to adopt semantic web technologies. Many organizations are providing the same services and could easily adopt a common “API.”