That's what the article says. But Knight was mostly overturned by Swift. Wikipedia has a decent overview of US antitrust law.[1] The ongoing question is the extent to which courts and the Justice Department should look at the economic implications of sheer size.

If you just grow to being #1 without acquiring your big competitors, that's generally OK in the US. It's competition, not collusion. Google never acquired Yahoo or Bing. Facebook never acquired Myspace or Twitter. So there was no key merger to block.

European Union antitrust policy is based more on the goal of having several major competitors, so there's price competition. An EU study indicates that, below four competitors, the leaders tend to implicitly collude. But in industries with strong network effects, it's hard to have many big competitors.

A modern summary from a law firm: [2]

[1] https://en.wikipedia.org/wiki/United_States_antitrust_law

[2] https://www.arnoldporter.com/en/perspectives/publications/20...