I think webapps should be xml (with all the data to display) transformed into html on the client side with XSLT generated by framework templating system).
What a blast from the past. We did exactly this in '99-2000 (yes), and it was ridiculed as being over-engineered. At the time, it was the future because "XML will underpin all data transfer everywhere", and therefore we would be set up to run on any device, should any other device begin to exist. Needless to say, the winds changed way sooner than that became a real use case.
How would such a webapp make API calls and act on the responses? Even for a static website, HTML isn't very good at handling arbitrary sizes, which I think was part of the original motivation for React.
The developer experience was amazing, you could easily inspect the data backing any page. XSLT was hard but probably easier than React these days.
[1] https://getsymphony.com