He said something like: accessibility cannot be simply duct-taped on. It's a fundamental part of the core web technologies, that all the JS frameworks have obsfucated.
Nope. Dialog, progress, details, many input types, etc html tags are not very accessible by default and behave differently in browsers.
From the top of my head, you cannot get a proper date picker in safari using html alone.
You also need to change attributes to help navigate the user.
Mind you, accessibility goes beyond screen readers. You will need javascript for building gesture controls, keyboard shortcuts, etc which is very needed for people with restricted movements.
Many people will need UX feedback to understand what is going on. You cannot achieve that without Javascript. Animations, focus, etc are all part of usability and comes under accessibility.
Do a whole fix in one place for the benefit of everyone, rather than making every tiny website make a bunch of half fixes.
You will need to design your layout and order elements properly. You cannot patch it with aria- soup which many developers do.