By not allowing developers to patch their app 'on the fly', directly, without going through a new version in the app store (which is a very lengthy process, almost forever in security terms), Apple effectively protects their iOS users from malicious code (not from the dev, which is probably to be trusted if the app is already installed, but from MITM attacks and the likes). However at the same time they deny very hasty security patches, which may compromise the device and all associated data and accounts entirely.
So there's no best world but undoubtingly many aspects to consider. Anecdotally I find that it's often better to trust the developers of an app to maintain their own thing; the OS only being a facilitator, provided the user has control (UAC on Windows, Permissions on mobile, etc.) [note: obviously you trust the OS vendor to patch said OS, it's just a particular kind of app]
I believe carefully crafted update should mostly mitigate that risk.
Also current policy don't prevent app developers to implement a "kill switch" that will prompt user to update (or wait for update) at splash screen and abort loading the malfunctioning version.
By not allowing developers to patch their app 'on the fly', directly, without going through a new version in the app store (which is a very lengthy process, almost forever in security terms), Apple effectively protects their iOS users from malicious code (not from the dev, which is probably to be trusted if the app is already installed, but from MITM attacks and the likes). However at the same time they deny very hasty security patches, which may compromise the device and all associated data and accounts entirely.
So there's no best world but undoubtingly many aspects to consider. Anecdotally I find that it's often better to trust the developers of an app to maintain their own thing; the OS only being a facilitator, provided the user has control (UAC on Windows, Permissions on mobile, etc.) [note: obviously you trust the OS vendor to patch said OS, it's just a particular kind of app]
edit: wording