I can read, and you’ve already written that. But there are logical bits missing between your premise and your conclusion. Is there any measurable effect? Is say WhatsApp adoption rate significantly lower on iOS because of this? How much more anticompetitive is it than just bundling a SMS app with every phone?

Anything a company does to improve its market share is a reduction of competition, the threshold for anticompetitive behaviour is higher than that. Not saying Apple never does anything anticompetitive (they do), but iMessage is a very stupid hill to die on.