I made an interactive pitch comparison tool
This was just a fun little coding project, but I thought some people on this site might be interested. I took 2021 statcast data for each pitch thrown by each pitcher in MLB and measured a Euclidean distance-based similarity score to all other pitchers who throw that pitch. This measure is based on release speed, spin rate, horizontal break, and vertical break.
You can play around with the tool here.
One interesting insight I got from this tool: The most similar four-seem fastballs to Tyler Glasnow's were Pete Fairbanks and Drew Rasmussen. Rasmussen and Glasnow also have very similar sliders.