I keep seeing people make this claim and frankly I don't buy it. While I think it's true that a minority of users produce a majority of the content, I don't think it's necessarily the people on third party apps. I think it's total speculation that there's a large overlap.

My own speculation is that a majority of the content is produced by people using Reddit in a browser on a laptop/desktop machine. It's much faster and easier to produce content in this mode.