I think we ought to be thinking specifics, rather than simply 'harder!'
For example, I recently completed the first Thorm fight on top of Moonrise.
The fight is fairly easy but introduces us to Kethric as a commander. His necromites do focus attacks and hit the indicated target often, but that's it.
Other than moar minions/HPs, my suggestion would be targeted _reaction attacks_ by all necromites in range who see the target attack. The skilled player might have to spend a round saving a downed character early in the fight and adjust tactics accordingly.
However, we've got to recognise the elephant in the room: over-leveling and over-gearing. A higher difficulty has to have us at lower level than baseline and take away some of the go-to wonder-items.
