Anecdotally around 90% of the people I know in the UK (40s age group ) have Facebook and use it for something (even if it's just for checking restaurants/gigs etc), almost everyone uses Messenger or Whatsapp. Also for those saying they use Facetime, stats suggest that half phones in the UK are Android. FB is relevant, even if you want to be, maybe in the same ways Windows/Microsoft is relevant for a whole load of people.