Tried a campaign as France on medium for the lols. Its turn 37 now and I am at war with Milan, England, Denmark and Portugal. Kicking their butts in battle so hard, their armies still suck and they keep attacking without generals. I am excommunicated ofcourse, but I don't think I even care at all or will care in the future. I can easily take the happiness hits for my population and all my neighbours are at war with me already anyway. I have now taken Rennes and Caen which England controlled. I have taken Genoa and I am besieging Milan. Took Bruges from Denmark and besieging Antwerp or whatever settlement it is. I have been first ranked in everything since turn 25.
I gain about 8k a turn when I don't construct or recruit, which I always do. I have about two full stacks running around and apart from that just milita defending my towns. Prince Louis has full command and dread now, I am already pretty much unstoppable.
Dunno what you are doing wrong OP, but this is the easiest campaign I've ever played.