I cannot say much about people who don't show themselves and seem to not exist. Or who may be high skilled but where I cannot see the code. Isn't it always like this that if we evaluate someone as very good or even being one of the best that we mean of all people we know and where we can evaluate the skills?
The best way I can rate someones skills is by reading his code. Just seeing the result makes it much harder to evaluate how intelligently it was written. Small exceptions are graphic engines which can do stuff which was never possible before in such a radical new way -- Carmack also did this a few times but in most cases, the code was also released a few years later. (Only exception I know was Commander Keen. But it was obvious that he introduced something very clever and new here. And it was also not unknown how he did it after those games were released.)