More to the point, in my experience the kind of people who actually do great things are not the kind of people who spend their time thinking about how mediocre, unambitious and lackluster other people are.

It's not necessarily dismissing them. Face it, some people are mediocre and unambitious. It doesn't say anything about what kind of people they are, but it says something about how they are intellectually and how pleasant working with them will be.