FB's app is the product of a web-based service that's been transported to the mobile platform, while Path and Instagram are native to and created for mobile. While this is obvious, consider all the functionality that FB already had on the web that had to be transported into their web app; a ton of thought had to go into retaining FB's functionality along with the innovation inherently required of anyone who creates a new mobile app. The way they did this - while preserving their functionality and retaining FB's already established feel - itself required took much innovation.

Path and Instagram were created inherently for mobile, and have much simpler functionality models. I'm not saying that this should take away from the remarkable achievements that both have had, nor am I saying that FB's app doesn't need improvements, but perhaps that this is just an unfair knock on FB's mobile app/strategy thus far.