I'm wondering how do you folk even come up with this kind of optimisations.

Sheer stubbornness.

Profilers lie and some more than most. I’ve gotten 3x from code with a perfectly rectangular profile output.

Part of it comes down to a trick game devs steal from finance: give each task a budget and keep it to the budget even if it’s not the tall tent pole.

You should not spend 10% of your response time on telemetry and logging combined. Yet I pulled 10% TTFB out of just the logging and telemetry code on a project. It was a frog boiling situation. Every new epic used the new code and determining the cumulative cost wasn’t easy.