Having seen them both in the low minors at young-for-level ages, it's development. I see a lot of minor league games, and 95% of the dudes who look like that at their ages in high-A become at least above average major leaguers. Robles at least got better on defense.
To give you an example, one of the best players I saw in high-A last year was Michael Harris II. Like Kieboom at that level, he looked like he had a couple things to work on at the plate to allow him to handle breaking stuff and hard stuff under his hands, but not much else. Difference is, a year later that looks fixed and he's in CF in Atlanta. That's development, even if absurdly fast. Kieboom is no better on offense - same issues, same holes - and worse on defense.
Same thing happens with pitchers. Fedde in high-A looks like Fedde in MLB. Not so with dudes in other orgs.
our minor league organization is light years behind our competitors. the NYY are playing an entire different sport than us in terms of player development.
