But before Facebook did this Snap demonstrated that it's still possible to ladder up (https://stratechery.com/2016/snapchats-ladder/) from an initially seemingly easily copy-able idea into something meaningful - the reason why Facebook didn't copy Snapchat initially was because they didn't get it, and didn't see the threat until it was nearly too late.
There are new social network startups being developed every day, but the reason they don't succeed isn't because Google copy them - it's because they are trying to copy Facebook/Twitter/Instagram/AirBnB/Uber, not the other way round. Or because they suck.
Like I said before - if you develop your idea and the worst that happens is that Facebook copies it, then that's actually a really cool outcome, as by then you've probably done extremely well. The more likely outcome, as I suspect you well know, is that it is ignored by everyone apart from your closest friends.
p.s. Here's another Ben Thompson article about the Facebook monopoly. The real reason FB is a problem is because they own the digital representation of our real relationships, and no startup is going to be able to compete with that https://stratechery.com/2017/facebook-and-the-cost-of-monopo...
Btw, I know plenty of non technical people and teams that use Slack.