That's a good way to put it. Plate discipline can be taught and can change as players mature and gain experience. But there's no guarantee. Sometimes there are negative consequences of trying to be more discipline (we may have seen that with Bo to some extent). Undiscipline hitters also seem to decline faster when their physical skills (bat speed, flexibility, etc.) start to erode. Discipline hitters are often better at knowing what pitches they can handle (given new physical limitations) and which ones they can't.
That said, Robert is still young enough that you probably don't need to worry too much about a physical decline and there's certainly potential to get even more out of him. As is, I'm not sure Robert is on the same level as someone like Soto, Betts, etc. - where you're willing to give up all your top farm system guys to acquire. I think his value is inflated because of the contract he's signed and the potentially excess value is provides. Then again, I didn't think Yelich was either and he went on to post B2B 7+ WAR seasons.