Assume everything else, like the quality of the content, would stay the same as now
This would tell us if social media content behaves like & should be treated as a commodity (just like magazines & DVDs), or something completely different like waste or like a public good
This is a non-sensical question. On a social media service YOU are the product. You’re characterizing the content as the product. But the content is merely the advertisement or bait for users, who are the real product, being sold to advertisers and countless other organizations. Why do you think reddit started charging for API access? Same goes for ads on Facebook, Google services, Instagram, TikTok, etc.