You're assuming the same thing you're arguing for. Namely, that JSON should be your base format. I can equally say:
"I understand that everything in HTML could also be represented in another format. But if your master data is in HTML, does it always make sense to convert the data to JSON just for the sake of it? Would you build a separate client-side rendering component only for that conversion?"
There two non-circular considerations that favor HTML:
1. Web pages still render via DOM. JSON data has to be tramsformed, HTML does not.
I am arguing that no one format SHOULD be your base format for data. You'll happen to have a format or another for any reason, it could be json, xml, csv or anything else.
Contrary to that you are positing that everything should always be based on or converted to plain html before serving to a browser. That's the point where we disagree.
"I understand that everything in HTML could also be represented in another format. But if your master data is in HTML, does it always make sense to convert the data to JSON just for the sake of it? Would you build a separate client-side rendering component only for that conversion?"
There two non-circular considerations that favor HTML:
1. Web pages still render via DOM. JSON data has to be tramsformed, HTML does not.
2. HTML has semantic capabilities. JSON does not.