I played around 35ish turns as the Saga faction so far. Early on, it seems better to have artillery with more traditional units. The AI routinely fields armies with around 1/3 sabre cavalry and the rest being a mix of line infantries, levy infantries and spear units. These units are inferior to spear levies in a melee and don't really have the firepower to wreck them before they close in, especially after being thinned down by artillery. The spears protect the artillery easily from all the sabre cavalries and the artillery thins out the infantry units.

I'm pretty much playing with a few general units, mostly spear levies and 1 parrott gun in my army. I'm only just starting to recently add line infantry.