Do you consider Nippon Professional Baseball to be on par with Major League Baseball; that is, would you consider them both to consist of (lower case) major leagues?
A lot of questions that people treat as complicated, or controversial, could be answered quite easily if there were clear answer to that question. I happen to think the Central League and Pacific League are not on par with the National League and American League -- but your mileage may vary.
A common conception is that the Japanese Leagues are comparable to Triple-A baseball in the U.S., though Clay Davenport concluded otherwise in 2002).
Anecdotally, I can think of more players who came here from Japan and didn't live up to the hype than players who came here from Japan and exceeded the hype. On the other hand, this may be because high-profile players made the leap before rank-and-file did; for example, nobody in the U.S. expected great things from Hideki Okajima.
On the third hand this gets to why I (chauvinistically?) put U.S. Major League Baseball alone on the top tier: Many of Japan's biggest stars wish to play for U.S. teams; the converse seems not to be true to any extent. Free agents generally go from the U.S. to Japan for lack of U.S. major league opportunities, rather than as a result of getting bids both places and finding a Japanese bid to be superior.
Anyhow, practical implications for how you answer the main question:
Should 30-year-olds who played several seasons in Japan be considered for the MLB rookie of the year award? I strongly believe they should (in large part because in fact they are clearly eligible).
Is it noteworthy that Ichiro now has a combined 3,000 hits between the Orix Blue Wave and the Seattle Mariners? Sort of -- but only sort of. I don't know off-hand how many home runs Henry Aaron hit at any given level of the minors; it says here that Barry Bonds had seven home runs at high "A" and 13 more at Triple-A. There's a good chance that in 2010 Jack Cust will hit his 300th professional home run.
Posted by Matt Bruce at July 30, 2008 01:31 PMI'd think that cultural issues and lack of financial incentive also hamper movement of players from the US to Japan, and may be more of an issue than the relative competitveness of both leagues. The current trend of NBA players going to Europe seems like something worth comparing, given that the players leaving the NBA are fairly analagous to the level of player that usually winds up in Japan.
Posted by: Mark at July 30, 2008 06:24 PMHey, at least credit BTF with the subject inspiration!
Posted by: Keith at July 30, 2008 08:10 PMOut of curiosity, where do/did you stand on Calder Cup eligibility for Sergei Makarov and Wayne Gretzky?
Posted by: Greg at July 31, 2008 06:28 AMSince the Calder Trophy specifies "first year of performance in the National Hockey League," I'd be pro-eligibility (easy decision) though I understand where people who disagree are coming from. (I think they're wrong on the face of it but I understand the spirit.)
Posted by: me at July 31, 2008 10:20 AM