> You're much more likely to encounter regressions when doing this under time pressure.

There is nothing to suggest you should wait to optimize under pressure, only that you should optimize only after you have measured. Benchmark tests are still best written during the development cycle, not while running hot in production.

Starting with the naive solution helps quickly ensure that your API is sensible and that your testing/benchmarking is in good shape before you start poking at the hard bits where you are much more likely to screw things up, all while offering a baseline score to prove that your optimizations are actually necessary and an improvement.