A common argument against Rob's claim that the American League teams are superior to National League teams is that AL teams have an innate advantage in interleague play purely as a matter of rules. Some seem put off by the idea that the American League simply has more talent that the National League right now. Therefore, they are looking for a way to explain the AL's interleague dominance without admitting that the AL might just be better at the moment.
The argument goes like this: American League teams must have a designated hitter throughout the season, so they make an effort to acquire a good one. The National League teams do not do this, and so bat a much inferior player as a DH when they play AL teams in AL parks. However, AL pitchers generally bat nearly as poorly as NL pitchers, so the advantage is not returned when AL teams visit NL stadiums. Thus, NL teams are at a net disadvantage when it comes to playing AL teams.
On its face, this argument seems sound. I believe that it is also incorrect. Allow me to elaborate.
Certainly, if the only difference between two teams were the quality of their DHs, the team with the superior DH would be at an advantage. Certainly, we would expect the American League to have better DHs than the National League. Others have tried to argue that the DH rule does not give American League teams an advantage, but in the long run, if the only difference between the American and National Leagues is the quality of their DHs, the American League must be said to have an advantage.
But should we assume that American League teams and National League teams ought to be equally talented apart from the DH position? The question here is solely that of whether or not the existence of the DH gives American League teams an advantage in the total accumulation of talent. In other words, does the existence of the DH allow American League teams to field teams genuinely superior to National League teams?
What do I mean by "field a superior team?" I mean simply that unless the existence of the DH rule allows American League teams to accumulate more expected win production on their teams, we will have no reason to expect them to be superior to National League teams. On average, the teams will be of equal quality. The DH rule will not bias talent distribution towards the American League.
Let us assume that every team has an equal budget at the start of each year. Let us further assume that every single player is a free agent at the start of each year. Finally, let us assume that teams make correct determinations of player value. Clearly, each team should end up of equal quality since they all have the same resources, the same pool of players, and have all valued each player correctly. So, how will the DH rule change the talent distribution between the American and National Leagues?
The American League will certainly have better designated hitters. After all, they are worth more to American League teams. However, they also consume resources that could have gone to acquiring non-DH talent. The National League does not have to budget for a DH. Thus, they can devote more resources to acquiring superior non-DH talent.
There is an opportunity cost to spending money on a DH. National League teams do not have to pay this cost. American League teams do. Thus, while American League teams should have superior DHs, the National League should on average be superior everywhere else. Thus, while American League teams will have a superior team while the DH rule is in effect, this should be balanced by the fact that when the DH rule is not in effect, National League teams will tend to have superior players at every remaining position, this giving them the advantage.
What if our assumptions did not hold? Well, if the first assumption, that of equal budgets, isn't true (and it isn't), the conclusion doesn't really change. If the American League is superior because its teams can purchase both high quality DH talent and high quality non-DH talent, the cause is not the existence of the DH. If the DH went away, the American League would still be superior because its teams could devote more resources to non-DH players.
If the second assumption, that of perpetual free agency, is not true (and it isn't), the conclusion still does not change. There may be fluctuations due to timing in the talent market that give American League teams a temporary advantage. However, this same timing could also swing the pendulum the National League's way. If too many American League teams end up with too many resources committed to underperforming DHs, this would definitely be the case. On average, this should not cause the DH rule to favor the American League.
Finally, if the third assumption, that of perfect talent valuation is not true (and it isn't), the conclusion again does not change. If National League teams are inferior because they are inferior at evaluating talent, this is not a strike against the DH rule. It is a strike against National League front offices.
So what can explain the current gap between the two leagues? Who knows? Perhaps this is simply some cyclical variation. Perhaps American League teams have cultivated a resource advantage over National League teams (the AL is home to the Red Sox and Yankees, after all). Perhaps AL teams have been luckier in the draft.
The bottom line is that wins are wins, no matter how you get them. Therefore, teams should be willing to pay the same amount for a win no matter where it comes from on the diamond. The American League simply has to allocate its resources differently, but this should change the fact that, like National League teams, they are simply trying to maximize the number of wins they can accrue with the resources they have.
Over the long run, the DH rule cannot explain the difference between the two leagues.