As always, such statements are general (and my original quote used the phrase "almost invariably").
Instead of trying to provide a full answer to your question (well, OK, I know NOTHING about your personal aspirations), let me ask a question: What proportion of your personal playing ability is due, in your opinion, to "professional instruction" that you have received?
I suspect it would be: "little or none."
Although I don't know anything about you personally, I DO know that MANY MANY MANY very good players have never received any formalized instruction at all.
I'll also add: there are surely many people who are FAT, who are STUPID, who are OLD, or who are POOR who play pool, really, exceptionally well....let's say...better than many/most instructors, lets say. To me that suggests (and I can elaborate more if necessary) that the main path to playing well is only the intention and dedication to get there (I'm not talking about the US open here; more about, "the best in town" etc). From that point I tend to infer that most instructors STEPPED FROM THE PATH of trying to play to their ultimate ability, and instead chose to concentrate on giving instruction instead. Am I really wrong about that, you think?
Furthermore, to put this (minor point, for me, in this discussion) issue more practically: In modern academic science, those who are best in research (i.e., is REAL SCIENCE) are almost exclusively involved in research....while those less suited to actually carrying out the process of science invariably end up...."teaching."