The difficulty in playing nomadic factions isn't in their unit roster, which tends to be top-notch, but their general lack of infrastructure. You can only build basic ports, level 1 mines, low level farms, etc. Thus, while you might have good units, you'll find yourself frequently outnumbered by the AI. Add to that the heavy nerfing of cavalry and missiles (And the strengthening of infantry and phalanxes) and you will find nomadic campaigns very, very difficult. The exception to this is the Pahlava, who get Persian reforms as they expand into Iran, allowing them to upgrade their settlements further and recruit a more diverse roster.