I think they'll claim security for Messages. I don't have nearly enough information to know if they can win that particular issue, and it sounds like there are reasonable arguments on both sides. But they don't have a monopoly on messaging — WhatsApp is huge, Signal and others exist. I don't think Apple lets you use Siri to send messages via other services, or at least they didn't used to let you. But other than that they are granted near parity on iOS.