The benchmarks are not invented by the LLM, they are from an issue where Scott Shambaugh himself suggests this change as low-hanging, but low importance, perf improvement fruit:

https://github.com/matplotlib/matplotlib/issues/31130

Ah fair enough. But then it seems the bot completely ignored the discussion in question, there's a reason they spent time evaluating and discussing it instead of just making the change. Having a bot push on the issue that the humans are already well aware of is just as bad behaviour.