In the future, if you’re going to argue something we can all easily look up, you might want to read your supporting sources past the first five words.
Enormity as a synonym for enormousness is sometimes considered an error, though other usage guides hold that there is little basis for the distinction. Both words ultimately go back to the same Latin source word ēnōrmis meaning “deviating from the norm, abnormal”.
So the meaning of "enormity" is closer to original than "enormous".
is based on the number of the population in each country who are members of a Christian denomination or who identify themselves as Christian, plus their children. It says nothing about the number of who actually believe in God and are regularly in the church.
South Korea is a bit of a different story. There actually are a lot of believing Christians in South Korea. About 30% of the total population is Christian, making them the 5th most Christian country in Asia as a percentage (after East Timor, Cyprus, Georgia, and the Philippines), and 6th in Asia in terms of total number (after Russia, the Philippines, Indonesia, China, and India), but 34th worldwide.