Instagram's user experience is/was great--it lets people feel like they're doing something significant and artistic in only a few seconds. I think that's the most important aspect behind Instagram's growth.
Is a strong product a "hack?"
Even 3 is arguable as it's just uploading the photo before capturing the meta. YouTube has been doing that since I can even remember.
Since when is following good convention, and doing what you're supposed to do considered a hack?