Not being a pain here but can you explain why myocarditis is dangerous in his case (that he has to miss the whole season) but when someone gets myocarditis from the vaccine we were told it's not dangerous and entirely treatable?
		
		
	 
I'll try best I can.  Without knowing the specifics of what he has, we can't say for sure. 
First of all, there are different levels or severity of myocarditis, much like most things.  Myocarditis, in general terms, is simply inflammation of the heart muscle.  With the reports I've seen about myocarditis from the vaccine, which is mostly in teenage boys, it's a mild inflammation that typically has no clinical significance.  Essentially, as a result of the immune response to the vaccine, there's some inflammation that is detected by blood work if it's done, but otherwise they may have zero symptoms and it resolves on its own without any issue.  It's very mild.
We already know that myocarditis happens more frequently with Covid than from the vaccine.  But, it also seems that it's typically more clinically significant, meaning they are more likely to have symptoms. 
In its worst form, myocarditis can cause death (we see that in kids when they get it from certain viral illnesses).  It affects the heart muscle so severely that is compromises its ability to function.  So, now imagine a spectrum of severity where it doesn't affect function at all to where it causes the heart to fail. 
So, if you want to assign a scale of 1-10, for example, what Archibald may have had could be somewhere in the middle.  Who knows how severe.  Who knows if it's actually affecting the function of his heart.  But, being a professional athlete and the rigors of his sport, it sounds like they are determining that he is at risk of having cardiac dysfunction when working the heart too much.  It may otherwise not affect him at all.  Again, can't say for sure.  And it's certainly possible that a teenage boy that gets the vaccine and ends up developing myocarditis could have enough severity to limit his activity if he was a professional player too.  But, more often than not, it's not an issue except for a minority of the minority that get it to begin with.
So, to summarize, myocarditis from the vaccine is typically less severe than myocarditis from Covid.  And the stress that being a pro hockey player puts on the heart is more severe than most other people such that he would be more limited than others.