Boswell’s metric of using overall wins is reasonable on the face. After all, we use total wins and record to decide which clubs go to the playoffs. However, it isn’t clear that total wins can be used to compare clubs in the National and American Leagues. Teams play most of their games against teams in their own league, so if the NL is far inferior to the AL in a given season, then total record would tell me little. After all, we wouldn’t say that the Tides are better than the Nationals if the Tides had a better winning percentage in a given year.
The way to test this is by seeing how the two leagues do in interleague play. When we do that comparison, it becomes pretty clear that total wins isn’t the best parameter to compare clubs in different leagues for at least 2016. Through 8/24, 266 interleague games were played. In those games, the AL held a 146-120 advantage. This is good for a 54.9% winning percentage and would put a random team in the AL on pace to win 89 games against a team in the NL. The average AL team would be a wildcard contender if they could just play against NL teams.
Of the 15 teams in the AL, only 5 are below .500 against opponents in their league. These five clubs have gone just 38-51 against the NL, resulting in a 42.7% win percentage. Against the AL, these five clubs have gone 232-308 resulting in a 42.96% win percentage. It appears clear that the bad teams in the AL haven’t improved their record by playing against teams in the NL. However, the ten teams in the AL that are above .500 have gone 580-504 against other teams in the AL for a 53.5% win percentage. They’ve also gone 108-69 against teams in the NL for a 61% win percentage. This puts top teams on pace to win 98.85 games against the NL. This indicates that pretty much any of the top teams in the AL would have the best record in the majors if they could just play against NL clubs. Unfortunately for them, that’s not an option.
In contrast, 8 out of 15 teams in the NL are below .500 against other NL teams. These teams have a 41.4% winning percentage against the AL and a 44.2% winning percentage against the NL. This is what you’d expect to see if the AL is stronger than the NL. In addition, the 7 teams above .500 in the NL have a 56.7% winning percentage against the NL and a 49.2% winning percentage against the NL. Basically, the story that this data is telling is that even the best teams in the NL are only as good as the average AL club. And these top seven NL clubs are largely padding their record by beating up on teams like the Braves, Phillies and the Reds. It’s probably no coincidence that Jimenez had an excellent outing last night because he played against an NL team. This chart shows the data above.
Meanwhile, while the NL is largely getting dominated by the AL, the AL East has shown itself to be the strongest division in the pack. At 278-263 against other AL teams, the AL East is the sole division with a winning record against the AL. This means that while the Orioles play most of its games against the strongest competition, the NL plays most of its games against weak competition.
The Nationals, in a division devoid of any quality competition, have staked themselves to a seven and a half game lead. They’re almost a lock to make it to the playoffs. To a certain extent, it doesn’t really matter. Each team in the division plays roughly the same schedule, so each team has a fair chance of winning their division. However, it does suggest that the Orioles would have a higher winning percentage than they do if they were able to play AAAA teams like the Nationals. Obviously, this suggests that Boswell’s argument is flawed. The AL is simply far better than the AL and therefore you can’t compare win percentage between two teams in different leagues. It probably means you can’t compare runs scored and allowed without controlling for the better quality in the AL either.
Per Wikipedia, a golf handicap is a numerical measure of a golfer's lack of ability. In match play, bad golfers are given a handicap so that they have a chance to compete with good golfers. Perhaps MLB should consider the same concept for inter-league play. They could spot NL teams a one run lead, or perhaps give them an extra out every third inning. Because it sure doesn't seem that NL teams can compete against good AL teams without some kind of help.