Really? So when you see Gandhi beside you while playing Rome, you won't build a big stack of Praetorians you KNOW he won't adequately defend against in order to take him out and get his lands? You don't Immortal/War Chariot rush, Quecha rush, Dog Soldier Rush, or even Axemen rush in situations where you know the AI won't be prepared? Sorry to say, when a human player sees the Romans beside them, they build tons of axemen in anticipation of the upcoming rush. An AI won't. This is a "logic fault," and a tremendous number of the ways we get up on the AI are 'logic faults' which it is extremely unlikely you don't use to your advantage every game you play.
Most people play this game, and win at this game, by exploiting the weakness of the AI... And they don't even realize it in many cases. When put into a situation where you know the AI either won't, or is very unlikely, to be prepared to have unit Y crammed down their throat en-masse, I'm sorry to say, you're exploiting the weakness of the AI. Half of this game is coming to recognize when the AI isn't programmed to deal with what you're sending it it. With the AI's technical advantage on higher difficulties (and I'm talking about higher than Monarch - the first BIG leap is Monarch to Emperor, in my opinion) you're not likely to ever beat it without pulling tricks to exploit its tactical weaknesses - whether it is temp-switching to a demanded civic on spiritual or forest rushing a dozen war chariots for an early rush... Or doing exactly what I've outlined here.
I would ask to anyone else who wants to come to this thread and say "Oh, it's an exploit - I play without cheating! Just drop a difficulty."... Please don't. Or, at least, before you do, and ask yourself seriously... How much of my playing isn't simply recognizing that "See that AI will not be prepared to deal with X and won't react in a way that would prevent X, and then send X at the AI until it submits?" And then, when you've decided this is a cheap exploit, go to Immortal, do exactly this, and tell me how easy the game is for you.