Hmm. This looks to me like a lot of the savings were realized by moving away from managed services into a scenario where there’s more operator overhead. The AWS bill gets lower, but what about the cost of the engineering work?
We've seen our teams go both from managed to non-managed and non-managed to managed with relative success - to give scale, across all of our accounts we spend way north of $3 million/month at AWS so this has happened within our realm a quite few times. The short, unsatisfying answer is that _it depends_. We have an internal policy from the suits that "if there's a managed version, use it" but most of our teams are thankfully smart enough to take that at face value and do their own analysis.