> you'd still basically always want to make the changes incrementally, system by system, and with a sensibly sequenced rollout plan rather.

Depends. It's significantly faster to deploy everything at the same time and accept that unlucky requests might end up in a weird state than to safely sequence changes.

In SRE phrasing, I'm choosing to spend our error budget to maximize change velocity by giving up on compatibility during deploys by skipping a multi-stage rollout plan. In return, I can condense a rollout to a single commit and deploy. A 99.9% availability target yields up to 86 seconds per day to pretend that deploys are "atomic".