No, it is not 100%, 125 or 150% upscaling.
It is the difference between the old cleartype, and the new font redenring.
Look at this page ( http://prohardver.hu/forum/index.html ).
It uses small size fonts, and in Edge (Spartan) it is nearly unreadable. Firefox is in the left, Edge is in the right.
Okay, I know, that Microsoft gets older and older, they're using glasses and larger fonts in every windows version (this forum has nearly twice the size of the font, compared to prohardver), and in 12, 14 font size, the new rendering is nearly acceptable, but, please, I want to use my PC with smaller font sizes...