No doubt Josh Gibson was an all time great hitter, but I think @McGarnagle makes a very valid point. The record keeping in the Negro Leagues during his era was spotty at best. Then again, if MLB has vetted the records and think they're valid, who am I to disagree. MLB is usually pretty particular about its stats.Most baseball historians consider Josh Gibson every bit the superstar that satchel Paige was.
On a related note....This is a great book.