The difference between liking/enjoying and gaining benefit I think is crucial here. It's akin to the difference between pleasure and happiness. No doubt the vast majority of people (if not everyone) on social media gains some pleasure from it. But as far as increasing happiness, aiding in quality of life and well-being and similar measures, it - in general - does not move the needle and not infrequently pulls in the opposite direction (in the absence of personal bonds).
The other important difference is between using social media sites as "literature" (i.e. not interacting with it but just consuming its thought-provoking and useful content, as you mention) and as a conversational medium. The former - in the absence of obviously harmful content like people showing off and then comparing oneself to them, or outrage porn, ect - is as far as I'm aware harmless and has a similar profile to reading in general.
But the constant one-off interactions, like this? It hits different. We know that consistent interaction with the same person - even if it is light meaningless interaction - has benefit. One study that comes to mind is of the daily interaction between customer and cashier every morning at the coffee shop. Believe it or not that has a statistically significant (though by no means large) positive effect on a person's mental state. Deep personal one-off conversation in person also have a significant benefit, at least in the short term.
But this - whatever this is - generally doesn't. Of course everyone is different, and obviously not everyone uses it exactly the same way, so there are outliers. But also human beings are talented at lying to themselves about the effects of things on them, often in the direction of exaggerating or inventing a benefit (and also failing at the afore-mentioned differentiation between pleasure and happiness). That's one of the big problems that researchers in outcomes studies on any number of things have to deal with. Objective observer and close other ratings of a person's happiness after say therapy or anti-depressants are often wildly less rosy than the person's self-report. We humans are often not good at being honest with ourselves.
But you are right about the "attention economy" context. We - near worldwide it seems - have little perfected the art of leisure. Our institutions have failed us, and we in turn have created little to take the place of the old ways. Our choices are too often between similarly poor options. That's probably why work and over-work have remained as popular as it has - what lies outside of it is too often stupefying. Which is one reason why I'm here now, talking with you, embracing (or stomaching) this momentary pleasure in what is perhaps a trade-off with a bit of my happiness.