> A typeface does not have a meaningful functional role in a document
100% incorrect. There are fonts that are made specifically to increase legibility for a dyslexic audience. If that's not a functional role than I don't know what is.
One dyslexia font was tested and found to have the same legibility as normal fonts:
"Dyslexie font neither benefits nor impedes the reading process of children with and without dyslexia."
https://link.springer.com/article/10.1007/s11881-017-0154-6
I'm skeptical that any of these fonts actually make a difference. (Although if you like Comic Sans, you might as well continue using it; it doesn't do any harm.)
Oh for God's sake. You also can't set an instruction manual entirely in DIN Grindel Milk. The implied subtext was the functional equivalence of free and unfree display fonts. The most popular dyslexia font in the world is free.