While a preponderance of story/explorer/normal players is one explanation, I think the bar for nightmare might be something along the lines of "Auradev is able to clear this, so it's theoretically winnable." Which would explain why the game became harder after the turn orders lost randomness, why the festival purification strategy got nerfed after we started talking about it on the forum(I rather liked being greedy with that one but respect the position of it being an oversight), and why new (plunderable) additions to the game seem to come with a reduction in loot elsewhere.
It should also be noted that the deluxe edition has a built-in cheat console. This might be skewing the perception of some patreon players.