That's actually pretty much talk. Daggerfall was pretty simple.
Daggerfall was very easy an combination of two effects.
No real high end enemies, you could sneak kill daedra lords in one hit at high level, enchants used fixed spells but many was somewhat level scaled so you could get magic immunity at higher levels.
Level scaled like Oblivion, however with an twist, you had an very low chance of running into real high level enemies at any level
I say Morrowind was hardest at low level, I also find Skyrim hard at medium low levels but Lydia helps a lot.
Oblivion was hardest at high level.