The law (Sherman Act) does actually say that “Every person who shall monopolize, or attempt to monopolize ... any part of the trade or commerce among the several States, or with foreign nations, shall be deemed guilty of a felony.” The test you mentioned is basically an attempt to explain the meaning of this contentious word “monopolize.”
> Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors. That is how that term is used here: a "monopolist" is a firm with significant and durable market power. Courts look at the firm's market share, but typically do not find monopoly power if the firm (or a group of firms acting in concert) has less than 50 percent of the sales of a particular product or service within a certain geographic area.
The Sherman Act is not the only relevant law here; the Clayton Act is relevant as law. (And was passed because the Sherman Act was too narrow). You do not need to be a monopoly to violate the Clayton Act, and most antitrust legislation nowadays is I believe brought under that and not the Sherman Act.
In this case the Sherman Act is relevant because all of Epic's federal claims are brought under the Sherman Act. (There are some California specific claims too.)
However, it is true that some of Epic's claims were brought under Section 1 of the Sherman Act which do not necessarily require monopoly power. (Section 1 has to deal with unreasonable restraints of trade, whereas Section 2 deals with monopolies.)
