The document published by the DOJ make the point that Apple has closer to 65% market share of you to by revenue, and also have a high market share amoung the teens. But I don’t get this focus on whether or not Apple is a monopoly. The lawsuit alleges that Apple has a significant market share is using anticompetitive practices to stay there.
Do you have some specific examples? I read half of the PDF but I don’t have knowledge of case laws that would be relevant.