i see a lot of people complaining about the AI whilst upping aggressive settings, not just in this thread but others too. personally in strategy games i have usually found that putting the ai on aggressive actually makes the game easier not harder.
sure in the very early game the player might be put under extra pressure by early war decs but assuming you survive that early game period the AI will cripple itself declaring unprofitable wars. if you make them aggressive they will declare wars that are likely to end in stalemate or at best be very hard won simply because their behaviour settings force them to and will end up losing most of their fleets time and time again for little or no gain.
what you actually want is them to behave more like humans and only declare profitable wars, as in ones they can win with relatively few losses unless they have absolutely no choice but to declare a more risky war or else stagnate.
try leaving the aggression settings on normal and see if the AI does any better.
note i am not trying to defend the AI here, i am well aware of how crap it has been, just pointing out that i generally find upping the AI aggressiveness is more of a hindrance than anything else to the AI in the long term.