Some dungeons in the past have been nerfed because people couldn't handle the sudden increase in damage. Stone Vigil is one of them. And mostly because it's required for story progression.

And increasing difficulty may be difficult across the board when you have people struggling on the following dungeons:

Stone Vigil [normal]
Dzemael Darkhold
Aurum Vale
Pharos Sirius [normal, even after the nerfs]
The Keeper of the Lake [mostly on the last boss]
Wanderer's Palace (Hard) with bad healers and tanks
The Vault
The Great Gubal Library [normal]
Bardam's Mettle
Doma Castle
Castrum Abania
The Burn

In short, average player skill may need to go up if you want dungeons to have increased difficulty.