Because of the DH, AL teams can more easily acquire offensive-minded players without worrying about their negative impact on defense.That's true, but let me add a couple other factors. First, the presence of a DH allows American League teams to sign long-term contracts to free agent hitters who, by the time their contract expires, probably won't be suited to play in the field. Albert Pujols is the Angels' first baseman. He is 34 and under contract through 2021. Prince Fielder, until a season-ending injury, was the Rangers' first baseman. He is 30 and under contract through 2020. Do you think Albert Pujols will be a first baseman when he's 41, or Prince Fielder when he's 36, especially since both players have battled injuries in recent years? Or consider the past winter's marquee free agent, Robinson Cano. He's 31 and plays second for the Mariners. Plays it well, I might add--he ranks highly in both traditional and advanced fielding metrics. But he's also signed through 2023, when he'll be 40. Doesn't it seem likely that by then he'll be at least a part-time DH by then? National League teams can't sign batters to those kind of contracts, because by the end of the contract, there won't be anywhere on the field to play them. Fine with us, fans of National League teams might say, given that paying Pujols $30 million in 2021, or Fielder $24 million in 2020, or Cano $24 million in 2023, is likely a money-losing proposition in terms of return on investment. But in avoiding those high-cost out years, National League teams are missing out on the near-term years when the players are good. That tilts the balance of power to the American League.
Here's another, mundane reason: The average American League payroll is $109.8 million. The average National League payroll is $104.9 million. (Both figures from baseball-reference.com) Might it be that the American League is better because they pay more and therefore get better players? And before you can say "Red Sox and Yankees," if you exclude those two teams from the AL totals and the Dodgers from the NL, American League teams still have a higher average payroll, $98.9 million to $97.2 million.