I've never lost either. I generally end up with a ranged + AoE combo, the AI can't seem to handle ranged very well, I don't even need summons for it. Once I get a few catapults it's usually game over for the AI. If I go straight melee it can be a little tough, but there's still so many ways to skirt around the AIs poor ability anyway.
Things that to me make the AI too easy:
They don't use teleport
Their Sov doesn't seem to ever use magic in tactical battle
They rarely use ranged units, so I can have 70 attack archers with 0 defense and low HP
They don't flank around to undefended cities, instead slamming into 200-300 power defended ones with 100-150 power armies
They spread 1-2 units out into all their level 1 cities that are doing nothing, instead of pooling them into a high value city
They build every building in every city no matter what. I also always see stuff like lvl 2 cities with 7-8 houses
They don't join up against a strong enemy, instead attacking each other more then me so you can be at war with everyone with no problem
They are basically playing gimped even on high difficulties, so its no wonder they don't do that well. All my games have been push overs after a certain amount of turns, unless I get bad luck on a starting spot and even then it's just a matter of reaching the first good AI city and taking it since it will have little to no defense.
Hopefully that's all easy stuff to fix.