I did check the contrast ratios for lots of sites, and medium fails WCAG in many places (subheadings, the UI buttons and more) even before you take into account the extra loss of contrast from super lightweight type choices.
The WCAG contrast guidelines were written before we had font and weight variation, before mobile phones showed web pages, and before even LCD screens were widespread .
If you measure actual contrast in practice on screen used in daylight or with ambient reflections it is much lower — the WCAG ratio doesn’t account for this at all. “pretty booklike’ may be true on your big desktop screen, but won’t be on phones or laptops used outdoors.
Medium body text is legible enough, yes, but it would be more legible if #000.