I have aslo noticed Archer Bombard makes AI less agressive because it tends to use it too much instead of standard attack, but I hate the all of nothing combat in this game so I will keep using it until I mange to mod combat mechanics to make units last more than one battle without killing or being killed (like in Civ VI).
One idea could be to give every unit a significant chance to retreat. AND already have mechanic to allow retreat while defending. It would increase the importance of retreating and healing, which might be yet another thing the AI doesn't cope well with.