@AVRC I am working to get a video on the Ai exploits up A.S.A.P. but I would like to comment on the few exploits that you did mention and explain how they can be replicated by the development team in the meantime while the video evidence is being worked on. As well as why myself and many captain mode players believe these exploits to be game-breaking issues.
Baiting the archers to switch to melee - Achieved by being the closest enemy unit within the Archers units melee range detection zone.
(Since you are the closest unit within melee range, All Archer Ai will individually try to defend itself from your perceived melee threat by drawing their own melee weapons and attacking you until you are either dead or have left their melee range.)
Getting all archery fire by standing in front with a shield - Achieved by standing in front of enemy archers and being the closest enemy unit located near to them and holding up your shield.
(Since you are the closest unit within firing range, all Archer Ai's will individually decide that you are the priority target and will fire at you exclusively unless another unit somehow manages to get closer to the archers than you.)
Baiting shield troops to break their shield wall - Achieved by walking back and forth either in front of or behind enemy shield wall formations with your captain so that the enemy Ai raises their weapons to strike you, but staying just far enough out of reach so that you never get hit by the Ai.
(When the ai is trying to strike you, their shield wall is broken and enemy archers can hit their exposed bodies. Typically effects only a few units at a time but you can walk alongside the line of shield wall to maximize how many ai break formation.)
Baiting infantry troops into pulling out their spears when it is not a good decision to do so - Achieved by simply bringing a Cavalry unit within melee distance of an infantry unit with a 2ndary spear just before a melee engagement.
(The ai pulls out its spears because the Cavalry units presence indicates that they should, but this is a trap/lure as this means your troops won't fight the enemy infantry with their primary weapons causing them to lose in the melee fight against other infantry when enemy Cavalry is also present.)
All of these exploits can be achieved by a single captain player unit and do not require multiple units to be present in order to happen. This is a huge problem in captain mode that we call "Ramboing" basically just meaning a player character splitting off from his Ai units in order to abuse and exploit the Ai's targeting parameters and behavioral patterns in a low-risk (only risking the players single unit) high reward (can potentially distract and destroy entire groups of units) strategy that diminishes the overall strategic gameplay of captain mode.
Another Potential Solution to Consider:
An idea that has been thrown around the community, originally suggested by Brandis in an older forum post, would be to Limit the distance the player captain unit can separate from his/her respective Ai units. A reasonable distance would be about 10 paces/steps or less so as to ensure that a player captain unit has to stay with his/her troops and couldn't run off on their own to engage in the exploitation of enemy Ai units with the above mentioned strategy as they would also have to risk losing their Ai units in the attempt as well rather than just a single unit, which would discourage players from using these "cheesey" strategies in favor of more organized and command based gameplay.
How to implement this?:
If a player captain gets more than 10 paces/steps away from his ai units that he/she has ordered to hold their position at a certain location, the Ai would automatically switch back to "Follow me" mode making it impossible for the player captain to leave his units unattended. This distance would still be reasonable enough to allow for players to maneuver around nearby their own units, but it would prevent players from separating from their units entirely and going off to exploit enemy Ai.
Thank you again for all your hard work I'm very grateful that your team is taking a look at these issues and addressing our concerns regarding this. I hope this is somewhat helpful, like I mentioned before I still plan to release a video with more details but I thought I could give you something to work with before that time comes.
P.S. Regarding Cavalry Ai improvements: A great way to improve Cavalry Ai would be to tighten their formation by reducing the distance between the Ai units as they charge. If the Ai would be capable of doing cycle-charges as a solid mass / blob it would be a lot more effective on the battlefield by being essentially a moving wall of deadly force. Just some thoughts I had.