Larry, I see your point, and Lou's too!..But keep in mind, super stars in any sport, would be hard put to find any instructor anywhere near their own equal.(skill wise)..However, assuming a player has established a good, workable set of skills, (for them) it then becomes strictly a matter of execution!..To my way of thinking, time spent competing with top players, can be far more rewarding than any top instructor can ever provide!
Instructors can only deal with mechanics and basics, (which is great for 'newbies') wheras only competing with top players, can expose you to all facets of the game..As I've often stated, you can practice until your arms fall off, but nothing can replace 'real live competition', for learning a complicated game like one pocket!