I hope with next updates AI gets improved on defence. Because right now AI never closes gates and on some factions never builds arrow towers and catapults (Dwarves, Rohan and Mordor for example). For me attacking AI is really easy right now.
I have never used battering rams because AI just doesn't close gates and two regular units destroy a building as fast as a battering ram.
Right now most of the time upgraded units and heroes are doing the dirty work. I only use catapults to destroy arrow towers (Isengard and Rivendell build arrow towers, Rohan only on camps), casue they kill my units fast.
If possible, I hope that in the future when I attack AI I need to rely on battering rams and catapults more.
Also it would be nice that AI also could but arches on the walls.