What makes someone a good mastering engineer? Well, it’s the same as with photographers (and any other artist): it’s never the gear but always the individual behind it. You can have the best mastering facility/studio with tons of expensive machines sporting it, there won’t be any good results when the person behind has no idea what to do and how something should sound. You need a very special feeling for what you are mastering. What’s its purpose, mood, approach?
Music, like every other piece of art, tells a story. You can tell this story understandable or not.