Some people become grandmaters before they are 18. I doubt that these kids study the game to the extent the IM does. This shows that you are born with the skill to improve and play strong chess fast or you are not.
To answer your question, it depends on the player's initial talent if or not it will be worth their while studing the game like this (In my opinion it won't improve their rating much). If a player has not improved their rating in a long time, they have reached their limmit. Studying the game they and night wont help them much from here. You are born with it or your not.
Chess is a game that teststhe player's abilities, not knowledge.
I was reviewing the history of an IM and noticed very little change to his rating over several decades. Is there anyone you know of that went from 1300 to 1900 over several years of learning? To what degree or percentage can studying the game actually improve ones game? What emperical data do we have on this?