Their rollout strategy is good.

I think you've misunderstood what they did

the flag was in beta for 5 months. And then they turned that on in prod for %1 users, still no reports.

It was in beta, had no reports, and then they turned it on for a subset of users, and created a flood of problems.

Well what better could they do?

Release it in a new version that doesn't auto-enable for small subsets of people, but is enabled for everyone if they've deployed that version. It's how software releases used to work. Enterprise environments can then test before it gets rolled, and save this problem from occurring.