I tried searching the source code to find out where it even draws the edit overlay. I could not find it. I don’t want to spend months learning the blender source code. So instead I decided to drop my idea onto the forum.
It’s my hypotheses that blender is blotting the vertices and edges using things like putpixel(). This has been historically very slow.
It’s my idea that replacing the vertice drawing function, with drawing cubes instead. I believe if the vertices are drawn as cubes, it would significantly increase the blender edit mode performance.