The thing about people abilities is that they aren't singular. There is no single skill that makes a guitarist exceptional, someone a 5 michelinAstar cook, or someone an exceptionally programmer. There is more like a set of skills of which some are more important than others. I would call some of them primary skills and some of them secondary skills. The thing about primary skills is that they are usually very hard to evaluate quickly, because they show their actually value in medium to long term projects. The secondary skills on the other hand are the skills helping the person express his primary skill easier and without unnecessary distractions.