Hard difficulty isn't that bad. In fact despite it being centralised towards abysmal like VH, it doesn't seem to move as fast, and if you have some Trade Rights/Alliance/ Same religion (i think) then it will increase towards perfect, albeit slow. On VH it would be stagnant, but on H its nice and even i guess.

I'm not totally sure, but i think the size/amount of armies the AI deploys also increases with campaign difficulty, since my first game on easy had them fielding half stacks all over and the one i play on hard has nearly full ones every time.