The AI
gives a fuck about their economy. They still have to pay for everything, they just get everything much cheaper.
As said:
Brutal means brutal and you can't expect to win against this AI. This is not only in this game like that - it's in many games similar. Our goal was something like that:
Easy - good enemy against beginners, they can win, but also can loose
Medium - stronger than easy, if you play from time to time and don't spam games you should be able to handle this AI most of the times
Hard - really hard for players who aren't playing often and a normal enemy for players who play a lot (means: you win most of the games, but can also loose)
Brutal: well... you die if you don't play much better and you have to expect hundreds over hundreds of units. Don't expect a fair game.
In nearly every game the AI cheats, have you played f.e. AoE? You never played against hard enemies as normal player, as it can spam much more than you.
Just don't play against brutal, but therefore against hard, when you think that brutal cheats too much for you.^^ Many people like to fight the brutal AI and win - and as long as there are weaker AIs for people who don't want such unfair battles, I think that there are no problems.