For instance, I went with running PostgreSQL instead of RDS because I have much more control over what's going on in the DB than I would with RDS.

But your point that the managed services don't require ops might be true in the short term, but what happens when something breaks? Or you experience a level of growth that expands past the capabilities of the services you've organized? There's hard practical limits to all the of SaaS offerings - mostly latency and throughput - that doesn't really come up in these discussions.

The analogy about it being like assembly programming might be more apt than I originally thought, given how not doing it yourself generally results in slower and poorly optimized solutions, but then "good enough" is often the mantra of the day at a certain scale.

As management tools mature and automatic, systemic optimizations are developed for SaaS systems, I wonder if the analogy will continue and areas where you need to manage it yourself to eke out performance and flexibility will get fewer and farther between over time.