Epic did their homework on the lawsuit, they make it very clear that Apple and Google are each separate monopolies. Because they have exclusive monopolies over app stores on devices that a large portion of people have. But the Play Store and App Store are not competitors: They control different markets.
Furthermore, Epic helped highlight a very important point about Android and iOS: They're not actually competitors. For an OEM building a phone, Android is the only option, it has a complete monopoly on mobile OSes with respect to the market of OEMs who might choose it.