It's a valid comparison, but it took Facebook more than a decade to get to $500bn, and Facebook also has over a billion users.  Steemit has a shot at that, but there will be MANY needed improvements to get there, and a LOT more onboarding of users.  But you're on the right trail, bc Zberg already knows about crypto and Steem, otherwise he wouldn't have printed his New Year's missive indirectly about Steemit, check it out...

https://steemit.com/bitcoin/@harpooninvestor/mark-zuckerberg-now-fears-steemit