There are 13 players currently on major league rosters from Japan, South Korea, and Taiwan. Of those 13 players, 9 are pitchers, and those pitchers have gotten off to relatively hot starts this season. Dave Cameron of FanGraphs wondered if we've been undervaluing pitchers from Asian countries:
Regardless, it’s time to recognize the great success that teams have had in plucking pitchers out of Pacific Rim countries. While they still get classified as prospects because of the lack of track records they have against Major League hitters, the performance of pitchers from these countries far outstrips anything we see from pitching prospects getting promoted through the minor leagues here in America. Of the nine active pitchers on the list, you could make a legitimate All-Star case for six of them right now. The success rate of this crop is absurdly high.
The list of pitchers Dave Cameron uses as examples includes Kyuji Fujikawa and Hisanori Takahashi, pitchers that have thrown less than five innings this season. A sample of that size probably isn't one that can be used to draw useful conclusions.
I'll also add that I felt the pitchers were grouped together rather haphazardly. While all of the pitcher's Cameron discussed originated from Asian countries, Junichi Tazawa is more of a product of the minor league system, having starting in AA at the age of 23 which isn't much different from where a college pitcher might begin their career.
Valuing pitchers from Asian countries much more highly than prospects who come up through the minor league system would be inefficient, in my opinion. Unless a team is willing to pay a costly posting fee, the majority of pitchers who come over from leagues in Asia are 30 or older. At that point in their careers they are much more injury prone and are more likely experience a decline in productivity. For the most part, pitchers who come up through the minor league system are much cheaper and a team is more likely to have them on the roster during the peak years of their career.