Sarisin i always play with your settings, in Light games were really easy on Monarch difficulty, now i'm playing on Fire and i have to say games are a bit harder due to the riders of apocalypse.Marathon at least favours a lot the player over AI because if you build one or two hero you can totally destroy the balance in your favour.Probably one of your problem is that you had too much civs in the map which easily make AC skyrocketing (like in my first Fire games i had AC going up to 60-70 on turn 500-600)
I'm now playing on Emperor, Huge, No Raging Barbs, 12 civs and No Aggressive AI and the game is a bit harder while the AC is a lot slower.
Try to play with less civs in the game, i would also advise to play without raging barbs turned on in Marathon, so some of the side effects like having superexperienced units will have less effect in your games for a better and balanced gaming experience.