To claim "100%" of pitchers who threw with the "inverted W" had career-ending injuries, one would need to produce video or photographic evidence of every major league pitcher who had ever thrown that way, along with substantiated newspaper accounts, or preferably, medical records, for every one of those pitchers.
Without that, it's unsubstantiated hyperbole.
The universe is the practical joke of the General at the expense of the Particular, quoth Frater Perdurabo, and laughed. The disciples nearest him wept, seeing the Universal Sorrow. Others laughed, seeing the Universal Joke. Others wept. Others laughed. Others wept because they couldn't see the Joke, and others laughed lest they should be thought not to see the Joke. But though FRATER laughed openly, he wept secretly; and really he neither laughed nor wept. Nor did he mean what he said.