I think you're exactly right. It has become a HN trope that every cost optimization story gets a response like this: your infrastructure costs are trumped by the cost of your developers, so why spend the expensive resource (developers) on optimizing the comparatively cheap bit (infrastructure). I'm tired of the trope because it's such an oversimplification.

What matters is the return on investment, and as you state, one of the great things about cost optimization is that its returns come largely risk free. By my math the optimizations described here return $100k a year. On a risk-adjusted basis, what task could this developer have performed that would have returned more?