Being able to spell correctly is really just a small piece of being a good writer or prosaist, perhaps even the smallest, at least insofar as that it's relatively easy and straightforward to fix. Likewise, the best speller in the world might be totally unable to string the words together into an interesting or even coherent whole. There is at least one Hugo-winning author that I know of who is dyslexic, and depends on first hunting the red squiggles in the word processor, and then sending of their texts to an editor for proofreading.