I think the story is to always benchmark first, and also to make sure your benchmarks reflect real-world use. What's dangerous is assuming something is faster without benchmarking.
I think many people reading that anecdote may come away with the idea that mmap is bad (and a monstrosity even) and read is good rather than your interpretation that you should benchmark better.
I dislike this kind of muddying the waters and I hope my comment provides another perspective for readers.
The whole point of the story seems to be that you shouldn't just read a story like this or the linked article and take away a simplistic data point like "mmap is faster" or "mmap is bad"
Best place to start is to have a good mental model of how things work and why they would be performant or not for a particular use case. Otherwise you're just taking shots in the dark.
