I'd be interested to know your editor's justification for thinking otherwise. Is this the professional editor you hired?
No, it was actually one I stole from Ernest. He claims it's from a general reading of literature. According to him, primary characters get referred to by first name, but secondary characters get referred to by their last names. When I think of that, I immediately think of Grisham or Ludlam. In this story, he focused (in chapter 5) on the main character's two bosses, who are grilling him for a perceived government fraud, so they're immediately seen as outsiders (though they play a role in his defense, and work to defend him). So far, I've changed a couple, initial references, but have kept the use of first names.
Strangely, where I expected him to flag something was when the character testifies before Congress. In those chapters, the legislators are always referred to by their proper names in dialogue, but when the characters speak among themselves, they switch to their first names.
Hell, even in business circles on Wall Street, I always referred to people by their first name, as the point was to establish a personal connect so they'll trust you, rather than an 'inferior' position of fear and distrust.
To put this into perspective, it's a past tense 3rd person omni perspective, focusing on the central character and those around him. I'm guessing it's a formal vs. informal relationship kind of thing, like the James Bond analogy. I'm also a sucker for sibling characters, so there's that dynamic in many of my stories as well.
Changing the topic slightly, in another story I have two characters with formal first names and pet names. As Ernest suggests, I use very short (two character) names. The lead character is "Al", and I never explain what his full name is. It's simply accepted as his name. However, everyone but he refers to his sister as "Betty", including the 3rd person omni narrator, but the lead character refers to her as "Be". I'm a little conflicted about consistency, but was hoping to develop the close ties between the siblings.