I think the point they're making is that you'd have the same problems with developers working HTML-first. Accessibility does not simply come for free in either situation, you need to make sure it's present.
Choosing, for example, whether to use a div with a click handler, or a proper button, is a decision you need to make regardless of whether or not you're using a framework.
So it seems incorrect to say that you lost accessibility in this case due to the framework. You lost accessibility due to developers who didn't understand the web platform well enough to design proper accessible controls. If they hadn't used a framework, they'd probably still not have made the site accessible.