If you want to crush the AI in the second age, it is very easy. You just need a few troops and battering rams.
If you want a more colourful and diverse gameplay and let it to age up, than because of the infinite resources of food and gold, the game doesn’t end. It generally turns to a stalemate or sometimes, when you get bored of this stalemate, and get behind the enemy AI, it crushes you.
So, right now, there is no point of playing the single player mode.
In aoe-2, where resources were limited, there was always an end to the game, in a way or another.
But in aoe-4, the AI just spams troops and siege units continuously whithout a break. There is no room for any strategy. Just spamming.