It's really a negligible difference in a per game basis. If you want to know why the NL has been decimated by the AL in interleague, I have a pair of very good alternative explanations for you - expansion and realignment. Expansion teams traditionally are much weaker teams initially, and they frequently dilute the pitching of the overall league, causing a rise in overall offensive numbers. The issue that is not often reflected is that those expansion teams carry very weak lineup themselves for multiple years as they build up a roster and farm system to sustain a workable major league lineup. In 1993, two expansion teams were added...to the National League. This was just prior to interleague beginning, and while these teams certainly were competitive quickly, the effect on other teams in the league in bringing down competitive level was certainly felt. In 1998, you have another expansion, adding yet another expansion team to the National League and one to the American League. The 1998 expansion brought with it realignment. The Milwaukee Brewers, who had been a team to win 92 games in 1992 just before interleague, moved to the National League at a time when the franchise was in a tailspin. From 2001-2004, the Brewers went on a 4-year run of losing at least 94 games each season, and their first season over .500 in the National League was a full decade after being added to the NL. Of course, we all saw the recent realignment. The Astros, after a full decade since the last time they won 90 games and 9 years since they made the playoffs, moved to the AL, and within 2 years, they were in the playoffs for the American League. Really, it's dumb luck as much as anything with both cases on realignment, but it certainly impacted the numbers. It's one big reason why I'd never utilize interleague numbers in any way as an argument for nor against the DH. They're not a good measuring stick as the league has been changing quite a bit and unevenly between the two leagues in that time.