Ambient occlusion is not only about realistic indirect lighting, but also about giving objects more depth. Great example here: https://developer.playcanvas.com/user-manual/graphics/lighti...

Also, looking just at inner corners of the room is too specific, SSAO affects creases everywhere, not just at the inner corners of the box.

These examples mention explicitely ambient light, which is the point of the article. SSAO makes no sense for direct ligth.