WhatsApp already replaced FB chat in various regions. And FB is already kind of a ghost town, beside elder 50+ new-comers who got their first smartphone just recently - in various regions. If you live in a filter bubble, where FB is still very on-vouch, great, but it depends on your friends and geographic. Many have the FB or messanger app still installed but rarely open it (because you can't even remove it from eg Samsung phones, only a few know that it's possible to deactivate it). That said, WhatsApp (the app) feels very cumbersome to use, compared to competitors from other countries.

So Instagram and WhatsApp are what keeps Facebook ahead. FB itself (the social network site) is probably past its peak (in various regions).