I'd contest claims of military stasis there - twice at the very least, the introduction of more professionalized military structures wrought massive changes upon the world - Macedon and the heyday of the Phalangists, and Marius' professionalized roman army and the resulting descent into civil war, downfall of the republic, etc.
Now, I agree that you could fit them all in the same game - and I think you could do a lot of really nifty things with the changing social roles of the military and those who fought within it. Indeed, both those professional forces had both their rise and their decline within that time-frame. Honestly, I think it'd be great for a game specifically because there were changes in the way war was done.