I analyze this supposed AL inferiority in this article on FanGraphs, and this one in Banished to the Pen. The FanGraphs article has data through games of September 5, while the Banished to the Pen piece is through September 9. The conclusion of each is the same:
The record level of parity in the American League to date has smoothed out the top and bottom of the league, resulting in hardly any notably bad or notably good teams. But that parity shouldn’t be mistaken for weakness. The American League is the better league overall, as evidenced by its clearly superior record in interleague play. The National League may have the best teams, but the American League remains the better league.