Especially considering how useful sleep data is, then I was surprised to see they're only getting sleep scores now.

My dirt cheap Huawei watches have had this for years. It's accurate enough (my own perception based on use). And I get a weeks battery life too (although I don't have the distracting fancy notifications perhaps). It does check blood oxygen levels, heart rate, stress etc.

I truly thought this was a solved problem (looking at headphones battery life, although I might need to check my assumptions here also apply to Airpods).