Playing simple maps (japan is a good example) against all-comers is a much sterner test of a team's ability.
The settings also make a huge difference. I have always advocated sequential, sunny, no cards and always play on simple, if often very large, maps.
So, the 'easiest' maps and the 'easiest' settings are the hardest to win well on (strangely), while playing the 'hardest' maps and the 'hardest' settings actually requires less ability.
