> it would be almost unusable at anything less than 13"

Native resolution on a 13" MacBook Air is already pretty unusable. Out of the box, the 13" MacBook Air (physical screen resolution 2560x1664) is configured with display scaling so that the “looks like” resolution is 1470x956 (i.e., macOS renders everything at 2x1470x956 – 2940x1912 – and then scales it down to match the display for output). If you dial the “looks like” resolution down to 1280x832 (so that the rendering resolution matches the output resolution; because, say, you prefer that every UI element not be a little bit blurry from being scaled down), you'll find yourself unbelievably short (ha) on vertical resolution. You basically have to turn dock hiding on. Even then, fixed-position headers are very common on websites these days, so between that and browser chrome, you'll often find that actual webpage content is crammed into the bottom half of the display.