It leads to a nice reading experience, but the HTML does not actually fully meet WCAG with for example too many heading level 1 tags on pages (sections are <h1> and should be <h2>) so there is an opportunity to upgrade the template to the latest and best WCAG has to offer.
Comment from @ajrgodfrey about the Rmd template:
Ref: https://www.w3.org/WAI/WCAG22/Techniques/html/H69.html