I don't know if or how this fits within actual antitrust law, but it makes sense that the issue was never price gouging, the issue was one entity gaining too much power.
In a theoretical dystopian future, a megacorp could own 99% of market share of all industries in the country, but intentionally offer very low prices on every product to avoid "monopoly" concerns. It becomes clear: monopolistic pricing is just a symptom, not the real issue. The real issue is power.
If this suit (and followup suits on other megacorps) fail, the future may call for new laws to define monopolistic power in novel ways, as soon as we the people recognize that getting search and email and social media for free doesn't mean that the megacorps are on our side.