The hypothesis is that the spike protein is causing the myocarditis. One would assume that the same spike protein in a live virus that proliferates in much high

The hypothesis is that the spike protein is causing the myocarditis. One would assume that the same spike protein in a live virus that proliferates in much higher quantities (since the mRNA version cannot replicate) would be much more damaging. Additionally, a small genetic change has been made to the spike protein code in the mRNA code to make it even less dangerous. So I would say the chances are very good that the myocarditis from COVID is both more common and more severe.