You can just map them all... I have. I also worked at AWS :)
But I wonder how much of their infrastructure is publicly mappable, compared to just the part of it that's exposed to the edge. (Can you map some internal instances in a VPC?)
That said, I'm sure there are a lot of side channels in the provisioning APIs, certificate logs, and other metadata that could paint a decently accurate picture of cloud sizes. It might not cover everything but it'd be good enough to track and measure a gradual expansion of capacity.
AWS has also disclosed 20 million Nitro adapters have been deployed, so you can do some backwards napkin math from that.
https://www.datacenterfrontier.com/cloud/article/11431213/sc...
A decade ago, there was a burst in construction and in some places the bottleneck was not getting the machines or electricity, but how fast they could deliver and pour cement, even working overnight.
Also how do you know their efficiency? Google might have less space but also a way to pack twice as much compute in the same place.
Like I said, this is impossible to know without a lot of insider information from a lot of companies.
Of course, it's all estimates. You can get fancier and count generators and transformers and stuff too.