> at a company that has reached the scale where employing engineers to manage self-hosted databases is more cost effective than outsourcing.

This is the crux of one of the most common fallacies in software engineering decision making today. I've participated in a bunch of architecture / vendor evaluations that concluded managed services are more cost effective almost purely because they underestimated (or even discarded entirely) the internal engineering cost of vendor management. Black box debugging is one of the most time costuming engineering pursuits, & even when it's something widely documented & well supported like RDS, it's only really tuned for the lowest common denominator - the complexities of tuning someone else's system at scale can really add up to only marginally less effort than self-hosting (if there's any difference at all).

But most importantly - even if it's significantly less effort than self-hosting, it's never effectively costed when evaluating trade-offs - that's what leads to this persistent myth about the engineering cost of self-hosting. "Managing" managed services is a non-zero cost.

Add to that the ultimate trade-off of accountability vs availability (internal engineers care less about availability when it's out of there hands - but it's still a loss to your product either way).