You need to use actual numbers. The total size of the active worldwide userbase on all of Facebook's platforms is at least one order of magnitude larger than reddit. And the revenue they extract from it is larger still. Reddit is merely the world's largest Internet forum. They don't have a moat.
Reddit is a top 20 site, according to Alexa. So they're not doing poorly. And any social website has a moat: the network effects from social connections.
It's at #18, below Wikipedia, live.com, Zoom, Yahoo, the usual suspects (Google/YouTube/Facebook/Amazon) and a bunch of Chinese websites.
All this proves is that the Alexa top N isn't a good metric of determining who is or isn't a monopoly. It's completely ignoring mobile apps (so Instagram/Whatsapp don't make an appearance), and it has no visibility into revenue. Reddit's current total valuation is in the small single digit billions. It doesn't deserve consideration in a conversation about the true gorillas in the field, i.e. the ones that are worth three orders of magnitude more.
