In the U.S. where this lawsuit was filed, Apple controls 50-60% of the smartphone market, where the next largest competitor Samsung holds only 20-25% [1]. Among U.S. teenagers the iPhone has a massive 87% market share [2]. That is indisputably dominant.

[1] https://www.statista.com/statistics/620805/smartphone-sales-...

[2] https://www.pipersandler.com/teens