These things are really hard to prove because any statistic cited within only one league is going to be off-set by the give-and-take relationship it has with its pitching/hitting/defense counterpart. Is a pitcher’s ERA low because he is that good or because the talent he’s facing isn’t that good? Pitching has been decidedly weak in the AL East the last year or so, but that could be because the offenses in the division are just awesome. And then, because the NL and AL don’t face each other that much, any data has to be taken with a grain of salt.
Vazquez pitched amazingly well last year and you’re suspicions about the AL-NL disparity are right, the NL doesn’t have the offensive prowess that the AL has. I think the AL has won interleague every year since like its inception and the AL has outslugged the NL to boot. But the difference isn’t so astronomically high that an NL Cy Young contender will flip leagues and suddenly become Carlos Silva.
And even if that were true, it would mean that any decent NL starter who got flipped to the AL East would be worse than Vazquez, and that’s false.
Here’s a few players who jumped onto the AL East ship in the last few years and have succeeded.
http://www.baseball-reference.com/players/m/millwke01.shtml AL West to AL East
http://www.baseball-reference.com/players/o/ohmanwi01.shtml NL West to AL East
http://www.baseball-reference.com/players/b/beltrad01.shtml AL West to AL East
http://www.baseball-reference.com/players/d/drewj.01.shtml NL West to AL East
Now just pitchers from the NL East to AL East:
AJ Burnett could go here too, but nobody likes AJ Burnett.
If you look at Vazquez’s peripherals, the stats that underlie a good or bad ERA, Vazquez is getting beat by some bad luck. His home run to fly ball ratio is at 22%, which is twice as much as the league’s standard rate, as well as Vazquez’s. For every five flyballs, he gives up one home run. The rest of the league gives up ten flyballs per home run. You may be thinking, “Well, maybe that’s just because he’s been that bad;” HR/FB rates are almost universally constant. The more flyballs a pitcher gives up, the more likely he is to allow home runs. Vazquez’s flyball ratio is way up from last year, which would explain some of the discrepancy, but the HR/FB rate is too high.
Vazquez’s BABIP is at a ridiculously high .349 (career .309) while his line drive percentage remains at career levels, so even if the ball does stay in the stadium, it’s somehow finding the grass more often than the outfielders mitt. His left on base % is at 62%, which is lower than both his career and the league’s averages (~73%), so runners on base are scoring more often than they should be. He’s suffering from the same problems that Justin Masterson and Cole Hamels are suffering from.
If you correct for these things, he’s still not great, but he’s not the worst pitcher in baseball.