It is, absolutely, possible to make an accessible web page with javascript. It is an order of magnitude (and I mean that literally) more likely to happen with a plain HTML page.
I think you're underestimating the capabilities assistive technologies have for dealing with dynamic UX.
Apps can be accessible. Video games can be accessible. The claim that any experience delivered in a web browser should, to enhance accessibility, remove and simplify interactivity down to just hyperlinks and forms, rather than support assistive technology in the use of more advanced interactions, seems completely defeatist.
