The American League continues to dominate the National League in head to head competition and have for several years. The AL has a .571 winning percentage over the NL this season.
We have one more week left of interleague play in the 2012 season, but to be honest, we don’t need to wait for the rest of the games to play out to realize that the American League is once again putting their dominance on full display. The AL and NL have squared off in 168 of the 252 scheduled games so far, and the whippersnappers in the American League have pounded their senior circuit brethren. The current totals: 96 wins for the AL, 72 for the NL, good for a .571 winning percentage. It isn’t just a few close games going the AL’s way either, as they’ve outscored the NL 776 to 659.
With 84 games left in interleague action, the National League would have to win 54 of them to avoid a ninth consecutive losing record against the American League. Even if the NL manages a split in the remaining games, the AL would finish with 138 wins, matching their best interleague mark since 2009, and the third best mark either league has managed since interleague play began. It’s not quite as bad as it was in 2006, when the AL went 154-98, but it’s clear that the American League is still the superior league.
Since 2005 the AL has a .556 winning percentage against NL teams.
Cherry-picking since 2005, the AL has won 1075 games and lost 857 to the NL, for a win% of .556. Only 4 of the AL teams are below-.500 against the NL. Only TWO NL teams are above .500 (Rox and Cards). So, it’s not a “oh, Yanks/Sox” excuse. It’s widespread.
This is why WAR is calculated slightly different for each league. Average in the NL is 2.0 wins above replacement while it's 2.5 wins above replacement in the AL. In other words, a league average player in the NL is a 2.0 WAR player while it's 2.5 in the AL. It's the far superior league and has been for awhile.