I think the focus on Stories is a huge mistake. Disclaimer: I'm too old to "get it". I've only used stories a few times, they feel like a huge time sink vs a normal FB/IG post, and that investment seems less worthwhile for something that doesn't stick around like a vacation photo album that I or someone else might refer back to later. I've only used stories when (say) traveling solo, and I want to post more mundane shit because I don't have a ton going on. Keeps folks at home more apprised of what I'm up to, but not the kind of content that's 'important/curated' enough to keep forever.
So on to why I think it's a mistake. Yes, both the core business and the stories rely on the network effects of social networks to gain/maintain popularity. But encouraging users to share ephemeral content makes the switching costs much lower. If some new "yourspace" competitor came along, I'd be hesitant to switch because I LIKE the library of content myself and my friends and family have built up over the years. If literally all that prevents me from switching is where my friends are, I can use both until everyone switches, and then just drop the one entirely.
Don't get me wrong, Facebook is still almost worthless to users without friends using it, but the switching costs are still higher when there's old content.