Inventiveness and compellingness are orthogonal. Facebook's mobile applications are excellent. They don't feel like a crippled, compromised version of Facebook. They feel like Facebook. Instagram and Path have the opposite problem: their web interfaces are second-class.
Perhaps. But their web interfaces will improve. Both are pretty small companies that will grow.
My main question is: Will something that "feels like Facebook" be what people want on their phones indefinitely? Or will something that feels more like a mobile app/service take over?
Facebook's mobile apps do feel like mobile apps. Sure, Path is prettier, but claiming that it's significantly more usable than mobile Facebook requires some objective substantiation.