It's not just the rate that's anti-competitive, it's that these two companies have stifled competition in mobile app distribution for over a decade now.

There is no viable competition in this space because Google and Apple never allowed for real competitors to the App Store and Play Store to exist. You have to use the App Store to distribute mobile apps on iPhones and iPads, and if you want automatic updates, background updates or batch installations/upgrades on Android, you have to use the Play Store.

These days, if you want to install an app whose developers didn't pay the Apple tax, macOS will make the app appear radioactive, and as if it is either broken or malicious. Same goes for Android, where apps distributed outside of the Play Store invoke scary warnings, and are hindered when it comes to automatic updates, background updates, or batch installs.