It is not just the AI, even if the AI use shield wall properly, AI armies get massacred by archers. Elite units should overperform, sure, but by how much should they overperform? The biggest issue currently is that archers are much more effective than cavalry and infantry in battles, so there is not point to recruit anything different to archers, except if you want a 100% cavalry army due to speed. Tier 5 archers should be similar than T5 infantry/cavalry units when we talk about effectiveness, but it is not the case currently.
Plus, try to get T5 cavalry units and then try to get T5 archer units, and then compare the huge difference. Getting T5 cav units require time, planification to try to keep them alive, and horses/war horses. To get T5 archers you just need to fight a few number of battles and them you get the most effective unit in the game without any effort.
Lastly, it is pretty bored to have to fight tons of battles where you do not even need to engage in melee because archers are able to kill everything from distance. Currently my archers are able to kill 70-80% of enemy armies from distance which is not intended for sure. Archers are removing any possible difficulty from battles, and making better the AI at blocking projectiles could help but it wont be enough.