Obviously, if you can pair top-level talent with the expertise of top-flight coaching, you'll produce a very, very competitive player. However, you have to have the talent in the first place.
I had the chance to work with expert coaches when I worked for USBC. They helped me to improve, but they didn't transform me into a world-class player. That's because I never had have enough natural talent to get to that level. They took me further than I could've gone on my own, but they couldn't transform me into more than my ability level can allow.
So, you either need to be exposed to great coaching from the very beginning so that they can build your game up from scratch, or you need to already have the ability inside of you. Even the world's best coach can't take a player with no ability and turn him or her into a superstar. They can only take them as far as their talent allows them to go. Think of it like Charles Barkley's golf game.