Well, as usual, it's somewhere in between what I said and what you said. You can break hitters at any level into some categories:
1. Those that won't ask for help or just go, OK, out of courtesy to the coach but won't try to change anything.
2 .Those that listen and try to make changes, but for one reason or another, go back to their old swing or habits.
3. Those that conscientiously listen and work diligently to make changes, noting what helped, maybe even documenting for future reference.
Whether it's Babe Ruth league age, or younger, up through the majors, players are just people and will vary all over the lot as students. Of course, guys that make their living hitting a baseball should pay more attention than kids.
The other team I watch a lot, the Giants, were leading the majors in hitting with RISP, and were near the top in many other hitting categories until about a month ago. Since then, they've fallen back to more typical Giants hitting ways and lost a 9 1/2 game lead to the Dodgers. On the one Giants message board I frequent, the poorer posters call for hitting coach Bam Bam Meulens head (and Bochy's, and Sabean's). All of those guys have been there a long time, but they (Meulens and Bochy) can't seem to do anything about the situation. Coaches can try until they are blue in the face, but they don't seem to be able to make much of a difference, in my opinion.