I’ll throw 2 other theories.
High school pitchers throw as hard as possible because radar gun readings over 95 mph translate into scholarships and signing bonuses. No one needs to throw 95-100 mph to get high school hitters out, but players do, often with negative results sooner or later. My prime example is Lucas Giolito, who had TJ prior to being drafted.
Also, Canadian pitchers seem to have a very high rate of injury. I’ve heard theories this is due to a shortened season in parts of Canada due to weather. And they’re not as prepared for dedicated baseball lives. Certainly our Paxton fits this, although the Sox other Canuck(Pivetta) does not. Others like Rich Harden and Adam Loewen absolutely do. But Paul Quantrill not so much. So it remains a plausible theory at best…