Baseball is probably the most difficult major pro sport to play, mentally. I think the potential mental impact from jumping a 20 year old international free agent from low A ball to the big leagues is being understated WRT Castro.
He spent most of 2014 in VANCOUVER. Not even Lansing! He had like, 170 total pro innings before making his MLB debut in 2015, and more than half of those literally came in Rookie ball. Before 2014, 73 out of his 90 pro innings actually occurred in the DOSL - in his home country!!!!
So irrespective of the "nuts and bolts" development (command, consistency, offspeed pitches, etc.) his mental development was also seriously truncated.
I'm not saying Miguel Castro was ruined by being rushed, but to downplay his being rushed is disingenuous. It's reasonable to think that if Miguel Castro had not been rushed, he would be set up for a much more effective and lucrative major league career at this point.
If the Rockies had decided to send him to A+ or AA in 2016 to work as a starter and develop his profile, who knows what would have happened. But they didn't, so Miguel Castro was shaken, like a baby, for the second time. It's hard to recover from abuse like that.
We can talk about things like this without talking in absolutes.