I think you're basically right, probability-wise.
That said, almost no one thought Kjerstad coming up today was the move they were going to make. So... you never really know with Mike and roster moves. But I agree, it's tough to figure out how he stays if Mounty is healthy when Hays comes back.
But he's 82nd percentile in barrel percentage and 92nd percentile in Whiff. I saw some some high EVs that were hit at 60 degree angles or more which were pop ups.
I'm not saying he's a long term piece. I'd need to see it for longer than two starts, but I like the stuff overall, especially if he can get his curveball over more often to give another look to the change and cutter.
The rookie is a #2 overall selection, now 25 years old, who battled back from missing significant time with non-baseball related illness, was called up last season but had mostly sit behind a mediocre performing veteran (Hays), and is performing better at the minor league levels than Hays ever did.
But, I guess he hasn’t paid his dues and is just temporarily holding a spot for the guy who was fortunate enough to come up when he was much younger and the organization was in bad shape.