I did the same test with 3 AI Cretan archers (3/6/4 chg/att/def) vs 3 hastati (2/7/14) abreast on flat map. The hastati have not had fire at will enabled in any of these archer tests so they don't throw the pila.
In the first test there was a glitch where the Cretan archers turned 90 degrees and marched off to my right. At about 45 degrees to my right they got stuck and couldn't move although I could hear orders being given by their commander. After 5 minutes of that, I turned my hastati line 45 degrees to face the archers and they started to move as soon as my hastati started to move. After some indecisive right/left movement, the archers organized one behind the other and advanced into firing range. They distributed their fire so as to reduce the hastati evenly by shooting at the unit with the most men. When my hastati were down to 45 men the first archer attacked my left hastati (the general's unit), but was routed. It rallied, made a second attack and routed again with 21 men rallying off to my left were it set up to shoot. At this time the second archer attacked the two hastati on my left while the third archer shot my right hand hastati. The 21 man archer then made a flank attack and my general died. All 3 hastati routed quickly after that.
In the second test, the Cretan archers moved directly forward one behind the other into shooting range. Once again they fired until my hastati were down to about 45 men. This time the first archer attacked my right hand hastati which only had 43 men. The archer routed and the second archer then attacked my lefthand hastati (the general's unit) which had been weaken further by archer fire, although my right hand hastati was the weakest one except it was set slightly bechind the line. The first archer rallied with 36 men and also charged my lefthand hastati while it was engaged and routed it on contact. The third archer (the AI's general) was shooting my right hand hastati this whole time and had it down to about 20 men. The first and second archers engaged the center hastati and routed it, and then quickly defeated the right hand hastati.
It all seems pretty reasonable except that the AI charges when it can't win.
Note: I forgot that I turned off fatigue.
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