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NPB stars are a far bigger part of the league quality though since they spend several years there.
Elite prospects are in and out and the vast majority of them aren't effective at the MLB level right off the bat. If half of them STAYED in AAA for several years, then ya the quality of AAA would rise.
All that said, I think the focus on star players is taking the discussion off course. How would a league-average AAA player do in the AL vs one from the NL or NPB?