You have activated the part of my brain that thinks only about the lost opportunity of emus as a medieval cavalry mount

See, the thing with horses is that they are really big. This makes them able to carry lots, but it also makes them imperfect for maneuvering. Meanwhile emus are lightweight and bipedal, making them extremely maneuverable, and a significantly smaller target for arrowfire.

Also a few thousand years of domestication could probably give them sword wings, but I won't get into that.

See I’m not crazy emus could easily replace trains