The problem is, this game is a sandbox game. With Rome 2, you often had some insignigicant tribe, with a limited roster and boring design taking over large chunks of the map. It took any real historical authenticity from the game, especially when playing as parthia and you see the romans getting conquered by the Etruscans.
I prefer fewer factions with a good design, rather than cloning a faction so many times which uses the exact same units over and over and over. Attila was even worse. Every barbarian faction was spamming full stack light spearmen.
Warhammer though will be different. Clone factions wont be positioned all in the same area of the map. I just hope the AI will use more than one unit type in their army.