What sort of battlefield will we be fighting on? If it’s anywhere other than an open flat plain, I’m sure I can find some pre-firearm culture from somewhere in the world that used effective camouflage. When one side is using camouflage and the other isn’t, and there are no enhanced-senses devices available beyond crude spyglasses, that’s going to be a huge advantage.
Well, if we are allowed cavalry - make mine mostly steppe nomad in equipment. As far as I can see, they mostly dominated any other combo of troops pre-gunpowder, however equipped.