actually these differences are already fairly significant.

at 6k, you already have to start pinching florins a bit and manage your economy instead of randomly building stuff.

the combat bonus also means that you have to maneuver and not just slam fairly equal units together and slug it out.

expert is by far the bigger leap though with even more economy management and also the crazier combat bonus.

I would perpetually vacillate between expert and hard as I sometimes just get sick of the +4 morale on expert which causes even peasants to reapeated rally

try modding it to have different florin levels though.

hard with 4k starting should be a good compromise.