I just don't buy that it's a special security concern at all. There are so many other possible security vulnerabilities to exploit that don't involve a JIT compiler. So why would Apple specifically restrict third party apps from JIT?
It's realistically just another way to ensure they maintain control over app distribution. Safari sucks for web apps. Third party browsers are just different shells over Safari on iOS. Apps built on things like React Native support hotfixing without slow app store reviews - but your app will be slow without JIT and rules force you to still go through reviews for feature changes.
There's no issue with any of this on Android.
