Benchmarks shortcomings are no worse... they inevitably measure something that is only close to the thing you actually care about, not the thing you actually care about. It's entirely plausible that this decreased benchmark score is because Anthropic's initial prompting of the model was overtuned to the benchmark and as they're gaining more experience with real world use they are changing the prompt to do better at that and consequentially worse at the benchmark.

Benchmarks measure what they measure. But your subjective experience also matters.