It's not about a level of quality. I can ask for my money back if the software sucks. I know when I download an app from the iOS App Store, exactly what the app is and is not allowed to do based on the sandboxxing that IOS does. I also know that the app won't have access to my private information without me giving it explicit permission when it tries to use it.

The "third party" I'm more concerned about is the random app developer. iOS prevents random developers from having access to files, the camera, the microphone, my music library, my location, contacts, my browsing history,using cellular data, draining my battery by processing in the background, etc. without me giving explicit permission.

Even ad blockers on iOS don't have access to my browsing history and you can disable third party keyboards from having network access.