Yea, its obviously rehearsed ... and why do they send out the samurai first by themselves? To make it more "historically accurate"?
I mean, I get fighting a battle piecemeal to detect for traps or to "try" and exploit a weakness ... but the initial charge (while kinda cool) didn't make much sense. And after winning, the AI samurai went back to their lines. HEREs an idea, next time an AI samurai charges, just place peasant spearmen to walk a bare yard in front of the rest of your army, and have ALL your Archers fire at the dudes (who are just randomly charging solo towards an entire army).
I mean, its kinda cool, but I could see it getting really silly/outta hand in a sandbox environment