But no one has ever argued that clutch is based on a player's physical skill or ability.
So if this is all 'clutch is not a repeatable skill' means, it's merely stating the obvious, and therefore tells us nothing.
I think we all would agree that being an MLB pitcher or hitter involves a whole package of skills, some of them physical and some of them mental.
The mental ones are obviously much more difficult to measure, but the fact they're difficult to measure obviously doesn't mean they don't exist.