I'd love to know how that was determined. Given that:
"If different fonts are best for different people, you might imagine that the solution to the fonts problem would be a preference setting to allow each user to select the font that’s best for them.
This solution will not work, for two reasons. First, previous research on user-interface customization has found that most users don’t use preference settings, but simply make do with the default.
Second, and worse, users don’t know what’s best for them, so they can’t choose the best font, even if they were given the option to customize their fonts. In this study, participants read 14% faster in their fastest font (314 WPM, on average) compared to their most preferred font (275 WPM, on average)"
https://www.nngroup.com/articles/best-font-for-online-readin...
What you actually want to compare speed in the most preferred font to, to show that individual choice is or is not better than one-size-fits-all dictate, is speed in the font that would be chosen as the universal choice by whichever mechanism would be used (to show it is universally better, show that there is no universal font choice that would lead to the average user being faster than with their preferred font.)
All comparing each individual's preferred font to each individual's fastest is showing that an individualized test-based optimized font choice is better for reading speed than individual preference font choice, which I guess is interesting if you are committed to individualized choices, but not if the entire question is whether individual or centralized choices are superior.
The (ex-)scientist in me is looking for a controlled study, ideally published in a peer reviewed journal, looking at - how can I put this - actual data.
60s of Googling gave me this
The effect of a specialized dyslexia font, OpenDyslexic, on reading rate and accuracy https://pmc.ncbi.nlm.nih.gov/articles/PMC5629233/
"A single-subject alternating treatment design was used to investigate the extent to which a specialized dyslexia font, OpenDyslexic, impacted reading rate or accuracy compared to two commonly used fonts when used with elementary students identified as having dyslexia. OpenDyslexic was compared to Arial and Times New Roman in three reading tasks: (a) letter naming, (b) word reading, and (c) nonsense word reading. Data were analyzed through visual analysis and improvement rate difference, a nonparametric measure of nonoverlap for comparing treatments. Results from this alternating treatment experiment show no improvement in reading rate or accuracy for individual students with dyslexia, as well as the group as a whole. While some students commented that the font was “new” or “different”, none of the participants reported preferring to read material presented in that font. These results indicate there may be no benefit for translating print materials to this font."
Advocacy for people with disabilities is important, but actual data may be even more important.