In DOS I had to manually draw every UI element.
Only in your first couple projects. By your third DOS project, you probably would have built up your own UI library.
But the big thing that DOS did better than Windows back in the early to mid 1990s was using all the features of the VGA. DOS applications could run in low definition (Mode 13h, Mode Y, and Mode X, with resolution of 320x200 to 320x240). This allowed updating the whole screen before Windows finished updating half of a 640x480 standard-definition screen. DOS could also use hardware scrolling to pan over a large virtual area without having to do the bit shifting bullcrap that plagued standard VGA mode back then. Both of these became less relevant, however, as CPU speeds and bus speeds rose and especially as graphics cards began to incorporate 3D rasterizers.