Font is perfectly readable on my retinas. On mobile so I can't inspect element, but the text looks pretty much black on white. #373737 should indeed be nearly black so that seems to match. Or is it the 15px height that makes it hard for you? It seems like a normal font size to me.
It's barely readable on my 16" MBP. Tiny font with super thin lines.
Zooming in is quite easy.
#373737 is over 20% of the way to white.
It's clearly grey text, not black.
Note the unit is px, not pt, it does not scale with devicePixelRatio.
Oh, yeah if the renderer ignores that the font is specified in a format not designed for displays with resolutions smaller than anyone can see anyway, that would explain the issue.