Market power and monopoly power are not the same thing. I will let the DOJ explain:
Market power and monopoly power are related but not the same. The Supreme Court has defined market power as "the ability to raise prices above those that would be charged in a competitive market,"(8) and monopoly power as "the power to control prices or exclude competition."(9) The Supreme Court has held that "[m]onopoly power under § 2 requires, of course, something greater than market power under § 1."(10) Precisely where market power becomes so great as to constitute what the law deems to be monopoly power is largely a matter of degree rather than one of kind. Clearly, however, monopoly power requires, at a minimum, a substantial degree of market power.
https://www.justice.gov/archives/atr/competition-and-monopol...
> Personally, I don't think DoJ is going to have a problem showing market power.
For the type of violation they have alleged (monopolization and attempted monopolization under Section 2 of the Sherman Act) they will need to show Apple holds monopoly power, or a dangerous probability of achieving it.
At its core, section 2 makes it illegal to acquire or maintain monopoly power through improper means. The long-standing requirement for monopolization is both "(1) the possession of monopoly power in the relevant market and (2) the willful acquisition or maintenance of that power as distinguished from growth or development as a consequence of a superior product, business acumen, or historic accident."
https://www.justice.gov/archives/atr/competition-and-monopol...