We were doing this with a team of sometimes one or two reliability engineers, but we were cheating, because our company culture meant that the engineers who built the systems are responsible for keeping them running, so they would invest their engineering time in fixing the problems along with us.

I personally found that runbooks were even worse for small size teams (like our four person reddit team) because they would get out of data even quicker than at the bigger places due to the rapidly changing environment.

I wrote down thread that if all of your deployment is automated than it is much easier to automate remediation, because you just change your deployment to fix the problem, as long as you can redeploy quickly.