The league wants to deny it but I think it tracks pretty well with hard slider usage. JV threw hard for years, no problem, he needed TJ the year after his slider usage exceeded 30%+. Max has gone longer than almost anyone without a TJ - has always keep his slider usage down (despite that he must have been tempted to use it more.) Sure there is lots of noise that makes it hard to get a strong correlation but when you look at the overall trend toward more breaking ball use, and clear mechanical logic that you must pronate to throw a slider, that's enough for me to make the assumption and say "prove it isn't true."