I think this may not necessarily be a surprise for you guys, but you can change the data set before starting the campaign (which is not possible in AOC/HD). I got a random cost data mod. This shakes up campaign difficulty in a very dramatic way: villagers cost gold. House cost gold. Farm cost gold. Trade Carts cost stone, and knights cost 1000 wood and food (!) while cavalier upgrade is free.
If someone think campaign in hard mode is still pretty doable, try out this random cost data mod and shake up your strategies.
Steam achievements may be forfeit, confirmed by the end score screen. The cost changes every day, so what works today may not work tomorrow. AI behaviour may change though depending on how it goes, including enemies.