I see where you're coming from and I agree with you overall, in particular how this is a first cut approximation. But I still want to nitpick the details a bit

I see where you're coming from and I agree with you overall, in particular how this is a first cut approximation. But I still want to nitpick the details a bit. If you want to determine whether there was a change in the failure rate, you need to use rate statistics - failures per service-hour. Your analysis is only using the numerator while we know the denominator (the number of services in GitHub that can go out) has increased over time - GitHub Actions and Packages are relatively new.