The point seems to be the author found very different estimates of just how much worse b-trees would be. As the author notes, hashmaps have some less desirable

The point seems to be the author found very different estimates of just how much worse b-trees would be. As the author notes, hashmaps have some less desirable properties as well. So the author ran some benchmarks to find out, and ended with the following conclusion: Overall, I'm unconvinced that it's worth exploring btrees further. I'll stick to hashmaps and I'll either iterate in insertion order or I'll require sorting entries before iterating.