a funny thing just happened i my pahlava campaign.
I had a spy near Massalia and rome and Lusotanna were fighting over it.
The Lusos had a half stack while the Romans had a huge stack nearby. And the romans attacked the Lusotana stack 7 times!!!! with small armies in the same AI turn. The Lusotana stack got a tiny bit smaller after every battle, but won all 7 of them, while the huge stack did not move.
If this happened to me, I would be angry as hell.