Data via BaseballSavant.com
As a follow-up to yesterday’s chart, here is a graph of aggregate pitch types in MLB since 2010. Pitch selection has been remarkably consistent over time; in 2015, all offspeed pitches are within 0.5% of their usage five years earlier. The exception is the sinker (which includes two-seam fastballs), which has fallen from 25% to 22% since 2010, mostly replaced by four-seam fastballs.
A significant caveat: Most pitch types exist on a spectrum, so MLBAM’s pitch classification algorithm is not perfect — especially for distinguishing between different fastball types. So the apparent decrease in sinkers could reflect changing classifications instead of a change in pitchers’ actual behavior. Additionally, my hypothesis is that the 2013 drop in sliders is due to a classification change (especially given the associated rise in curveballs), since it is out of line with all other years.