This is maddening to watch.
Props to Agrippa for making videos about a lot of different games, and having generally decent production values when doing so.
Having said that, this is a pretty great example of what not to do with an Age of Reason period army. He completely misuses his cavalry. To be fair, I see this in a lot of players; they believe a cavalry charge is to be used to create a breakthrough. It isn't. A quick check (as Agrippa constantly does during this video) in Pike & Shot will show very poor odds for cavalry charging formed, steady infantry. This isn't Panzers overrunning Russians during the blitzkrieg. Cavalry is for wrecking already unsteady, shot up infantry, preferably from a flank. Cavalry is for stopping the other guy's cavalry from doing that to you. Cavalry is for screening and scouting. Finally, cavalry during this period would have largely avoided melee in favor of closing, discharging pistols, and then riding out of range, a technique that could be used effectively in Pike & Shot.
The Jacobites had the best horse in Europe during the War of the Two Kings/War of the Grand Alliance. Tyrconnell's horse and associated squadrons of other regiments not only threw the Dutch te Voet infantry back at the Boyne, they nearly won Aughrim for James as well. It's a tragedy to see them handled this way.
Worse, he abandons good defensive positions held by his infantry and dragoons to cross the river. Oldbridge and the fords are very defensible. The Williamites can be bled badly trying to get across at Oldbridge, and at the very least delayed at the fords for a long time. More importantly, the Jacobite player can seriously limit the number of attacking Williamite units by holding the south bank at the fords, since only a single unit can cross at a time. If placed in cover, even dragoons can be effective in this role.
I blame Total War and similar RTS game franchises. Playing those abominations lures well-intentioned gamers into thinking they have a grasp of realistic military tactics. For the most part they don't. What they understand is how an RTS works, and that's completely different.
The most critical failing that RTS games encourage (and most other video games as well) is a complete lack of planning. Just a small amount of reading about this period will reveal that commanders from Conde and Turenne through Marlborough, Eugene and Frederick carefully planned their battles. These plans might not have always worked, but the Great Captains always had a plan and tried to implement it. Today's ADD gamers mostly just crash blocks of troops together and delight in the booms.
I like Pike & Shot for the miniatures feel of the game - it is, after all, derived from a set of miniatures rules. It does a decent job of simulating the warfare of this period, despite lacking leaders and formations. It's a good way to get introduced to Early Modern warfare. I wish more players would take the opportunity it offers to learn a bit when they play it.