The only faction that puts up a decent, unified and coordinate resistance is the senate. Therefore I argue that every faction should be applied with their behaviour for better gameplay. Occasionally a 9-10 star general seems to be more "in control" over his troops so modding in higher command levels is a viable approach too.

One of my most baffling encounters was the last king of the Iberians who came at me with a full stack. I had only 6 hast, 4 vel and 2 equ def a hilltop.
He marched his whole army in a nice formation, parked it some 50m from my lines, waited for a while like he was saying goodbye to his men. Then.... he charged will full force into my ranks and got killed instantly. His whole army now got very homesick and ran for the hills. I didn´t even bother to chase them down.