It's unfortunate that the word performance is overloaded and ML folks have a specific definition..that isn't what the rest of CS uses, but I understand Anthropic to mean response quality when they say this and not any other dimension you could measure performance on.
You can argue they're lying, but I think this is just folks misunderstanding what Anthropic is saying.
They didn't just drop cache. They elided thinking blocks even if you recache. That permanently degraded the model output for the rest of the session, even ignoring the bug, if you waited 60 minutes instead of 59.