Sure, but those are ultimately still players who don’t find the game too easy…
Also, some players despite AI cheats, and won’t play above a certain level due to them. It could be that the cheating on King is so blatant it makes people bored/frustrated with that level.
The cheating is actually not blatant on King, but regardless – wins on Prince are still only half of the wins on Chieftain. If many people refused to play on King or above merely because they dislike cheating then you’d see little difference between Chieftain and Prince, or even most victories on Prince. But you don’t.
We’re talking about an adequate challenge level for most players, so what 0.9% of players think is really not relevant. Someone always thinks any given game is too easy (or too hard).
You’re making an assumption that I don’t agree with: that everyone started out on a low difficulty and then continued to move up the ladder as they beat the previous difficulty, seeking the point at which they started losing.
Of course I assume that’s what most players do. Trying various difficulty levels until you find your comfort zone is the usual and sensible behavior, I don’t see what’s contentious about that.
However, I don’t even need that assumption. Observe that win percentages are monotonically decreasing as the difficulty rises, from Chieftain up to Deity. If all levels were equally easy for everyone, and all players picked a level at random, then you’d see equal win percentages for all levels which is not the case. So even if you assume that players pick levels at random, the distribution still shows that Prince is pretty challenging for most players.
You can say, however, that the number of players that managed to beat King were 1/5 of the number that managed to beat Chieftain. Whether they were the same people, no one knows. You already noticed this with your point about Settler difficulty victories compared to the higher difficulties.
And I also noted that Settler is special because it’s the tutorial difficulty level. The other levels are not tied to tutorials. Even so, Settler is still between Warlord and Chieftain so we’re not talking about some gigantic deviation here.