Earlier quoted context omitted.
For photos specifically, it takes me an average of 10 minutes to upload a photo on their iPhone app if I'm on my cell connection. The 10 minutes consists of a combination of upload attempts, fails, freezes, etc. It's just a horrible experience. If this new standalone photo app will let me easily, quickly, flawlessly upload photos to Facebook, then hell yeah.
This doesn't make any sense to me. Why not just fix the main app?
Ultimately I think it boils down to what you think of when you want to do take a photo or send a message which maps to (Facebook Camera, Facebook Messenger) more naturally than just Facebook.