I think this is a world view difference.
Personally, life experience has taught me that people never get better at anything unless they want to, and most people don't want to. This applies to basically everything in life.
Can you teach someone a boss mechanic? Sure. Can you teach them a trick to do better DPS? Probably. But as a whole, that's basically all they'll learn. If they aren't already interested in getting better by now, a month into the patch, they almost certainly never will because they are part of a self-selected group that isn't self-motivated enough to learn in the first place.
You can say this is defeatist or cynical or whatever and that's fine, but if you look at the way companies hire and whatnot, it's pretty much validated there, too.