WCAG 2.1 color contrast guidelines are a bit of a disservice to design. Color and contrast perception is much more complex than two simple ratios for small and large text.
Modern operating systems have tons of features that allow users to adjust text size, contrast, etc. Perception changes based on ambient lighting and smartphones adjust the display to those conditions. There are also different font weights, and fonts with different characteristics (like the fine lines of Bodoni), as well as effects like outlines and drop-shadows. As well as different use cases - reading dense scientific material strains eyes more than a quick scan of some news headlines.
WCAG 2.1 is like a blunt instrument. It can be a good starting point, but it's not the end-all-be-all (APCA is a good step forward). A more sophisticated approach also takes these other factors into consideration. Unlike designing for print, screen interfaces can be super dynamic and responsive and adjust to whatever the user needs and wants.
