It's weird that people never distill those arguments to their most basic logic.
Apple directly dictate the shape, speed, and existence of any innovation on iOS, and by extension, any innovation involving mobile phones or meant to run on mobile phones. They don't simply have "power" over it, in the sense that they get to say "Yes" or "No". iOS is locked down in such a fundamental way that any innovation will not come about unless Apple specifically envisions it and designs the OS to support it.
Browsers didn't exist when Windows 1.0 came out. But they happened. If it had been iOS, there would have been no networking, no JIT (I know that came later, bear with me), Firefox/Gecko could never have existed and been able to fix the web. Apple alone would have controlled the evolution of the most important tech of the past few decades. It couldn't have existed in the first place unless Apple, and no one else, invented it and put it in iOS themselves. Basic OS features: files and the filesystem, sharing, casting your screen, communicating with other devices. It doesn't exist until Apple makes it. It doesn't change until Apple changes it.
Even something as simple as file syncing. They forced Dropbox, GDrive, OneDrive to adopt their shitty, buggy backend. Those services all had to drop basic features to adapt. Those features can't ever come back unless Apple allows them. Any hypothetical new features won't exist unless Apple, and no one else, thinks of them and adds them.
How is this sane?