Statistical analysis has probably lengthened the game more than slow pitchers. Maybe we should limit the number of Ivy League stats majors that each franchise can hire to their front office!
Along similar lines, the number of pitchers used per game has increased by 1.0 over 25 years as those very strategists found utilizing more short relievers to be a valuable arbitrage for teams. This paradigm is best illustrated by the 2015 Kansas City Royals, who won their first World Series in twenty years on the back of no superstars and a very deep bullpen.
With more pitching changes every game, MLB should sooner reconsider the need to give eight warm-up pitches to relievers on the field and over two minutes to commercial breaks, as Will says in his column.