I wouldn't limit this to sword-sisters...
-less-than-optimal combat ai
- limited command ability
- lots of rough terrain
all mean that the only two options really available are an all-out-attack or holding a defensive position, and if you now figure in the terrain and the general ineptitude of ai cavalry when compared to ai infantry as well as the potential for hard-hitting ranged attacks fromt that infantry, it shouldn't be hard to conclude that:
defensive ranged troops with decent melee abilities>*;unless caught on an open plain, but that hardly happens, and even if it does you can normally redeploy your troops to a more favourable position before the enemy cavalry can hit you
The fact that the ai will always attack also helps, because they'll just keep running into that killing-ground you set up for them...
Now, if the AI used proper tactics and different types of troops could be given commands independently, this would be quite different, and combined arms would be much more useful than a one-sided approach...