The tactics of the Sengoku Era could be anywhere from extremely complex to extremely simple. One thing that I think would fit would be pre-determined, active formations. Aggressive formations, for example, which would start moving in a predetermined way with a click... And then, the ability to change formations with some sort of menu or hotkeys. Takeda 3 has this implemented in a somewhat poor, awkward way, but it's fun nonetheless. It wasn't the Takeda series, but the original Shogun that started the ball rolling on Japanese formations... but fell short. Same goes for Takeda. Nice try, but it fell short. I think the CA we have today, with its manpower and funding, could pull this off very well.
Aside from that, it would also make it easier for you to work with the AI. A predetermined set of active formations that it can switch back and forth to and from that actually make sense, that work the same for the player as well. Certain formations were used in certain situations, and it just makes a lot of sense to me.
[EDIT] btw it's obvious that the player should still be able to micromanage as they wish the way they do currently. I just think formations deserve an overhaul.
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