When you are talking about young pitching, regression shouldn't be a surprise, especially from someone who has been so up and down anyway. We saw the same from him last year. He was terrible for a large portion of the season with diminished stuff. That alone leaves the door open to it happening again.
Especially when you contrast what he has done with Reynaldo's time here being about as good as could be expected, having somebody regress isn't really that big of a surprise.
I will also promise you that Kopech will go through the same crazy ups and downs when he gets here. Don't be shocked when it happens.