Yes, it doesn't apply to
all factors. I only said: "
some things become easier on higher levels". Barbs and goody hut probabilities certainly don't.
For example:
a) A quick look at the HoF tables for Spaceship/Standard Map reveals that the finish date on the lower difficulty levels is faster than on the higher difficulty levels: Chieftain 550AD, Warlord710 AD, Regent 700AD, Monarch 1020AD, Emperor 1130AD, Demigod 1120AD, Deity 1200AD, Sid 1370AD.
This can basically be explained by the fact that the goody hut probabilities get worse with increasing difficulty level. On Chieftain/Warlord you basically build a few scouts and pop almost all ancient age techs from huts. On higher levels this is no longer possible, as you mainly get barbs from the huts... --> So clearly one example where something gets harder with increasing difficulty level.
b) Now taking a look at the tables for Domination/Large Map we see:
Chieftain 350BC, Warlord 610BC, Regent 450BC, Monarch 530BC, Emperor 350BC, Demigod 150BC, Deity 50BC, Sid 1600AD
So in this special case it looks like it is easier to do on Warlord, Regent and Monarch than on Chieftain! Only with Emperor it again starts getting harder. --> Here we have an "overlay" of two curves going into opposite directions: 1. Ability of the AI to fill the map with towns - this increases with the difficulty, making it easier for the human player to reach 66%. 2. Ability to take away these towns from the AI - this decreases with the difficulty, making it harder for the human player to reach 66%. Both curves combined explain the observed result.
And then there are also factors which make one aspect of the game easier and another aspect harder. Like the AI agressiveness. Trading becomes harder for you, but warfare will be easier for you, if the AIs have first worn each other down...
All in all, combining all these contradicting factors will result in a pretty complex mechanism. I guess that's pretty much what you say: difficulty level isn't everything...