My point is that the thing you would often do after that is go after people's iMessages anyways.
You don't need to access the messages app in order to get access to the messages.
it's the opposite actually, the messaging app needs permissions for the system level messaging component.
you're already root.
you can access any component without much restriction.
How the data is stored has nothing to do with this
Pwning the app will only provide access to whatever permission it has and we are still sandboxed.
Pwning a kernel module\driver will provide access to everything whether its messaging, call logs, pictures etc. we are not sandboxed, we don't need an LPE exploit.
I think the priority is clear.