90% of the time the AI should charge asap with all melee units, that would screw much more the player.
It amazing how often this happens.
In Mount and Blade, it was the same thing. When the AI enemies get into a nice formation and advance together, or decide to shoot it out, or order a cavarly advance and charge, there are ways to form your troops and crush them with practically no losses.
But when they have no commanders left, and just come at you in an amorphous blob of horses, infantry and archers, with random units charging, flanking, or running circles and shooting, prepare to lose half your troops, if you are lucky.
Of course, when it's players, it's a whole other story. Nothing I like to see better than players coming at our line in a blob. Mostly because with players, losing four fifths of your men is still a resounding win.