A month ago you would have been correct. The 25.9 update added many changes to Easy and Hard difficulty.
Still no hidden rewards for doing Hard mode, but some of us like a bit of challenge in our games.
From the patch notes:
**Hard Mode Difficulty Tweaks**
* Monsters no longer give you a grace period for stance moves, meaning group fights can lead to you getting swarmed much more rapidly.
* Using an escape skill now only gives you a grace period for the remainder of the turn instead of 2 turns.
* When charmed, escape skills have their odds cut down by 75% instead of 50%.
* When charmed, temptation checks have their difficulty increased by 5 instead of 1.
* Sleep drains 25% more energy from the player. * Energy costs to auto pass failed checks is increased by 25%.
* The minimum possible cost to auto pass a check is 25 instead of 10.
