What If Companies Get Big Because They're Better?

It's not clear. Antitrust policy only matters (in the sense of having positive effects!) in the presence of barriers to entry (non-contestability), and when these barriers are present it matters regardless of how the dominant firm got so big. So I think the folks who are pursuing this line of research are either confused, or at best they're reaching the same conclusions as mainstream scholarship in a very roundabout way.