Serif is meant to be printed, on paper, with the ridiculous DPI of printers.

These fonts have not been designed for pixelated displays. Yes, it's better on Retina / HiDPI displays (I even enjoy some serif fonts on those), but those have to be designed with pixels in mind. But they usually are atrocious on "classic" pixel densities.

And tangent: the print industry has a much wider typeface selection than "just" Times New Roman, which is rather rare in my personal experience (sample size of one, though).

Yes it would. People have no choice but to read college textbooks. They do have a choice when it comes to the usability of your site. You might not care, but you are not your users.

I'll remind you the criteria was "decent" not "possible to interpret."