I think they overestimated how much engagement the average reditter provides. Most people are consuming content, but not contributing any or posting comments or clicking ads or anything. 90% of engagement is driven by like 20% of users or some shit like that.
I suspect twitter is similar. But a difference between Reddit and twitter is how easily power users can migrate.
On twitter, you follow people. Power users were often cautious cause they didn’t want to lose their followers and non power users wanted to be where the power users are.
But on Reddit, you follow communities. For power users, there’s few direct followers to lose and for non power users, as long as there’s enough content, it doesn’t matter much who created it.