I checked my feed right now. First 20 posts: 8 are content created on FB (text, pictures snapped for uploading, etc), 12 are shares of external content. Hopefully you are right but don't underestimate a fact: the have not (the ones in the walled garden) won't see any of those content if they don't have friends on the open internet. And even if so, FB might choose not to show them content that they can't see anyway.