you should definitely be concerned that an odd spike in velocity suddenly went away and was followed up by recurring shoulder pain.
You might take some comfort if you believe the GM's explanation that they wanted to go very easy with him and give him an extended period to rest. If you buy that, then the 60 day DL shouldn't both you a whole lot.
But something like is a decent reason why trading pitching prospects, even for established pitchers, should not be inconceivable.
Soroka might well have hurt himself trying to put extra juice on the ball to get himself called up. Or not.
I wouldn't have traded him, but if he goes under the knife this fall I might well wish he had been.