I call bull here.
I consistently see things players can work on, it simply depends on the player's weaknesses.
I have no idea how hard they work, did Pivetta fail b/c of lack of work or his inability to generate movement on his FB and develop secondary pitches, is VV in the bullpen because of command or not working hard enough on his secondary pitches and so on. All I can observe are weaknesses/strengths and whether players improve.
Hoskins has to focus on hitting the ball to CF and not be pull happy.
Kingery when 100% has a quick bat but needs to improve his plate discipline.
Eflin needs to refine his command and work on a changeup.
Quinn needs to focus on taking advantage of his exceptional speed even at the cost of his average power.
Knapp just has to hit the way he did in college and the minors.
So when I say Quinn needs to work on bunting, it's in the context of his exceptional speed, Kingery should also do so but as RH it's less effective (extra step to 1B). Quinn's goal should be to become one of the best bunters in ML baseball, especially from the left side, because of the competitive advantage it gives him relative to most players. He should also be refining his swing to focus on contact, not power, for the same reason. The two are synergistic, if he bunts successfully on a regular basis, IFs will play a step in, increasing the probability of success from contact.
Whereas Hoskins should focus on improving his 1B defense, because few 1B are even average fielders, same with Bohm at 3B. So as above average hitters, getting to average or slightly above average on defense gives them a competitive advantage. But hard work is no guarantee of improvement, do they have the reflexes and eye to hand coordination?