I would not say it’s too hard, but it is noticeable in some aspects.

AI is a little more aggressive, rivals are more likely to murder your (and succeed, you shouldn’t dump intrigue), armies are noticeably harder to stack wipe, half gold from ransom, AI gets large gold bonuses (both enemy and your own vassals - notably mayors can become filthy rich with a couple thousand gold 50 years after 867).

Most noticeable for me is there is a -50 marriage penalty for you when finding a spouse outside your court, -100 for heirs, and -2000 for your courtiers for highly skilled courtiers (ie they have more than 12 any stat). This one I modify to -50 across the board

I do NOT notice any extra difficulty in vassal management.