I doubt you would need to do much in the way of changing formations or anything to make realistic looking historical battles in the scenario editor.
I think you can make very realistic looking battles without any mods.
As for the AI, it is generally stupid. I believe it usually sends them en-mass.
Currently retired from AOE3... moved on to LOTRO... yeah an MMO... but a fun one!
Hockey fan for Life:
"I believe the Canucks of Vancouver are formidable warriors." -Teal'c, Stargate SG-1