You didn't respond to the comment reply to you so I'll repeat - many users overlap. My original point stands - FB at 2B users monthly means they can't possibly be a tiny fraction because of the current amount of internet users especially when Google doesn't have a dominant share in China.
Plus you brought in other products/subsidiaries so then we have to include:
Messenger - 1B+ users
WhatsApp - 1B+ users
Instagram - 750M users
Of course I know the overlap is huge. Do you recognize you're wrong, is that why you didn't respond? That's fine then of course.