The most compelling part of this lawsuit is the ability to set default applications - specifically, default messaging applications. Apple could simply add that feature mid-lawsuit and completely derail Facebook’s efforts, though I don’t believe that will happen.
However, Facebook’s behavior is more indicative of a loss of power. Facebook running full-page newspaper ads and now a potential lawsuit was a foolish slip on their part: they revealed that their back is on the ropes. Whatever data Facebook is getting from people’s phones, it’s clearly the source of their power (with revenue being more of an afterthought). Facebook enjoys an INSANE amount of power by controlling the stories and images that are presented to its users. A quick Google search shows that people use Facebook an average of 58 minutes a day - that means Facebook gets 58 minutes a day, across billions of users, to inject any ideas they want. Entire societies are on an emotional rollercoaster as Facebook tries to find the balance between family chats, stories from old schoolmates, and emerging threats which can only be soothed with additional Facebook consumption and consumer spending. Now consider politicians and world leaders who want to advance a cause - imagine all they could accomplish with even 1 of those 58 minutes - injecting text, images, and video into people’s brains and who willingly put a screen 12 inches from their eyes! The distraction has become the method of delivery.