Even with an embedded model, SRE leadership is responsible, first and foremost, for setting up tooling like observability and auto-healing (i.e. Kubernetes) for

Even with an embedded model, SRE leadership is responsible, first and foremost, for setting up tooling like observability and auto-healing (i.e. Kubernetes) for the company's workloads, which gets you about 90% of the way there. If Product can't keep their service online because they never wrote tests etc., then the way you "bolt reliability on the side" is, SRE leadership gives the exec the raw lack-of-availability numbers (see: observability tooling), then the exec tells Product to stop fudging around and prioritize making the availability numbers better. Then Product management freezes feature development and takes a vacation for a sprint (or two) while Product developers focus on bolstering their QA.