> AWS was the public release of tooling that amazon had been bulding for almost 20 years at that point.
No, even at the onset AWS was an entirely-from-the-ground-up build. The only thing it could even be argued to sit on top of was the extremely crufty VMs and physical loadbalancers from the original Prod at that point, and those things were not doing anybody any favors.
Similar story for GCP.
All three of them had decades of institutional knowledge and procedures in place around running big services by the time Cloudflare was founded.