The ceiling is very high, the kid has a ton of swing and miss. McDermott as well. The control hasn't been good for them, but they both have high ceilings.
I have no doubt they are trying to the best of their ability. I don't think having Mayo or Holliday on the bench is going to find a 7th gear for them to kick in and try even harder. It's baseball, you're never as good or bad as you look most of the time.