While I agree with this to some extent, I think that without craft and learning, those authors won’t reach their full potential. Creativity is the fuel for the machine that is the writer’s craft. Schooling is important to fine-tune that machine so that the writer can get the best performance possible.
For example, I’ve read many stories that were written very well, almost perfectly, but the story lacked that certain something – that spark that set my imagination on fire. On the flipside, I’ve also read stories that were very imaginative and sucked me in, even if the writing itself was sub-par. As a reader, I can deal with either of those types of novels, but I’ll never call them favorites. The stories that really grab me have it all.
Just like everything else, writing takes practice, and the more you do it, the better you will become. The better tools you have, i.e. schooling, critique groups, conferences, and conventions, the better you’ll be able to craft and mold that creativity into something great.