> 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).

I'm really not sure what you're talking about here. I manage many RDS clusters at work. I think in total, we've spent maybe eight hours over the last three years "tuning" the system. It runs at about 100kqps during peak load. Could it be cheaper or faster? Probably, but it's a small fraction of our total infra spend and it's not keeping me up at night.

Virtually all the effort we've ever put in here has been making the application query the appropriate indexes. But you'd do no matter how you host your database.

Hell, even the metrics that RDS gives you for free make the thing pay for itself, IMO. The thought of setting up grafana to monitor a new database makes me sweat.