Could this not be more easily explained by the sharp declines in popularity of baseball? That players are stronger and faster is not a surprise given the huge spike in steroid use. But baseball went from the 'national past time' to a game that's been on a sharp decline for many decades now. Most skills seem to follow a power law, and so as you reduce the population playing something you greatly reduce the chance of finding the outlier among outliers.

Chess is a great example of this because it has no barriers to entry and an absolutely enormous player pool. And at the top there's this sort of oscillating pattern where everybody will be more or less equal, but then suddenly some outlier among outliers will show up and just completely dominant the game for many years, and in some cases even decades - to the point of being the best player across multiple generations of players.