> This is a 50% or more discount to the market-cap/unique visitor ratio of Twitter, Snap, and Facebook.[1] And all the stats I've seen indicate much higher user engagement and time on site for Reddit compared to the other social platforms.

Most people have one Snap / FB account and one, maximum two Twitter accounts... but throwaways are the norm on Reddit (as well as HN), which means Reddit's user count is inflated by quite a bit. Additionally, Reddit has large nsfw communities that draw lots of members and visitors (again, most with separate accounts!), and these can't be reasonably monetized at all.