Hmm. The task is so big it's hard to know where to begin. I'd say lower the scan range on shooters, so they don't abandon your vulnerable units to chase one horse on the far side of the map.
While your at it, figure out why a unit whose priority is enemy defenders spends so much time shooting walls and buildings while said defenders cut them to pieces.
Ooh, speaking of shooters it would be great if our armies would actually recognize command post archers as a threat, instead of letting them get dozens of shots off before responding. They seem to have no such problems responding to command post tanks.
I'll pass the baton to someone else now.
Yes! This is especially a problem when defensive units start attacking defenceless or otherwise unable-to-defend-themselves troops, like cannons or supply trains. At least with the former, the supply trains will start healing the troop which is being hit by a rogue spearman which my shooters seem to have allowed to slide under the radar. That will outdo the damage, but when that infantryman starts hitting my supply trains which neither heal themselves nor allow other supply trains to heal THEM, it begins to get annoying and it often results in the waste of a rally to kill that one soldier. Likewise, the command post archers need to become top priority, because occasionally they get off shots on two or three of my men before they finally notice and destroy those command post troops.
Also - what's with cannons deciding to break open additional walls? Most of my army, aside from one or two cannon(s), attack one piece of wall, which then acts as a strait for them all to pass through. However, there are usually a few archers, and a cannon or two, which have decided to destroy other sections of wall when they had no reason to do so. I've never had the problem you speak about with my shooters abandoning everyone else to kill faraway troops, instead, my supply trains are the problem. They insist on traveling across the map and willingly getting in the way of a gunman on a tower who picks them off easily. Why do they, instead of taking the longer, but at least safe, way out, suicidally charge like that?
Just had all three supply carts destroyed by two Chu Ko Nu that came out of a command post. Funny, well, actually not that funny, since they take 15 minutes to train.