They're in the top 6th among the world's economies, so I'd say that's reasonably prosperous, especially when you consider that unlike the US, Norway or Australia, the country has no natural resources to speak of, and 50 years ago, had a GDP per capita 2/3 of Zambia's, and 2/5 of Spain's. Note that in 1945, only 22% of South Koreans were literate. The last time this level of literacy existed in Spain was during the mid-19th century.
http://en.wikipedia.org/wiki/Trade_policy_of_South_Korea
Looks like South Korea is going the free trade route.
I now see your point that the economy there has grown, but now I reject your point that they are very protectionist.