What I'm missing here is a test environment. Gradual or not; why are they deploying straight to prod? At Cloudflare's scale, there should be a dedicated room in Cloudflare HQ with a full isolated model-scale deployment of their entire system. All changes should go there first, with tests run for every possible scenario.

Only after that do you use gradual deployment, with a big red oopsie button which immediately rolls the changes back. Languages with strong type systems won't save you, good procedure will.