The context is important here – when Xiedu was created, when Metataxер, when all sorts of Chinese maps that were discussed here. Naturally, now it is no longer the most difficult.
And then there is the question of whether difficulty is a goal in itself.
Regarding difficulty as a goal in itself. Personally, I am only interested in playing when the map is a challenge in itself. I can't even remember any simple and interesting maps. But with complex and uninteresting maps, the author of the "Rising from the Ashes" campaign came quite close to this combination :)
Guys, help me pass the battle in Xiedu. The Chinese pass this battle with the loss of only 3 griffins.
I don't have the opportunity to try it now, but I would replace the Crusaders with another single Griffin and, on the first turn, lure the dwarves into the lower right corner with the griffins, and drive the archers to the center from above, behind the barrier, covering them with the other two griffins. Then I would try to lead the dwarves around the bottom with the horses and shoot them, finishing them off at the right moment with the champions. We counter the curse with a blessing. The only question is the amount of mana and the moment when the remaining dwarves will be scared of the horses.