I think what Apple did with the App Store was remarkable, they won by being better. They were better by doing all of what you say, safe housekeeping, free code-signing, free dev tools, etc...
All of this allowed the creation of a thriving economy of apps on iOS. However, none of this means that the power of Apple isn't much higher today than it was when iOS was young and that they aren't exploiting that power. It also doesn't mean that the relationship wasn't symbiotic. That the devs prospered because iPhone prospered and the iPhone was prospering because the devs were building apps for it.
When iOS was only 5% of the market it could be ignored by a dev and that dev would be fine. Today you can't ignore iOS, you really just can't, that is a very different dynamic. This power dynamic is why Apple is getting regulated the way they are, they are too important now.