The only lesson to learn from this is that given exceptional resources and a long list of talent any stack can be made to scale.
That doesn't help most projects in the world.
That doesn't help most projects in the world.
Exactly. IIRC, Facebook itself is/was a giant ball of PHP, and they had to do all kinds of crazy things to make it scale, up to and including writing their own compilers and VMs.
That doesn't say anything about the suitability of the scalability of stock PHP.
Just keep moving forward unless the sky is falling is 100% the lesson to be learned here.
There was a time when "being web scale" was a real concern. That's one reason companies like Google make such a big deal about it in their technical interviews. Now most of the hard work has been done and exposed as services so today even an untrained teenager can stand up a web-scale service.