Worst still, they destroyed social media, perhaps even contributed to destroying mobile (destroyed in the sense that, well, they became dumpster fires).

I'm not sure a growth-obsessed Facebook could have done anything other than destroy social media, in the same way that a growth-obsessed Google couldn't have done anything other than destroy the web.

The only plausible alternate reality I can see would have been one where US anti-trust was vigorously enforced and kept Instagram and WhatsApp from being bought.

But that would have required expansions of US anti-trust law to allow for more proactive deployment.