Much truth in what you say. Studying the game is a big part of the equation. One thing I always noticed about the young Shane Van Boening is that he often sweated matches after being eliminated from a tournament. Even Efren used to say that watching other matches often gave him some new ideas to toy around with. Keep watching what others do, and you'll have a bigger library of shots to choose from when you're the one at the table.i don't know really how to measure the importance of instructors. the best young players in my part of europe don't have coaches or tutors in that sense, that part seems more organic here. monkey see, monkey do, and they tend to have other high level players in their clubs who they always practice and match up with. and these kids do watch a lot of pool too, both youtube and eurotour/kozoom.
i know that russia had a national coach for a while, maybe poland does too. other than that i don't know how prevalent it is. the technical aspects have never been trade secrets over here.
A good example of a very successful national coach is Alex Lely, who coached the players from the Netherlands for a few years. Alex' tutelage was a big factor in Niels Feijen finally getting over the finish line at the WPA World 9-ball Championship in 2014.