almost 2/3 of visitors to my Web site are from "mobile devices", so I have adjusted my pages so they display as well as they can on such devices - at least if they're Android and held horizontal. I'm not anxious to spend the money to find out how they look on i(anythings).
Google has moved me to their new (in development) "Mobile First" spider, which has found no serious problems and very few (and declining) minor issues. The site still works a hell of a lot better on a full screen, and is impossible to make significantly better on mobile devices.
A little more than 1/3 of my visitors are desktops, and maybe 5 to 7 are tablets.