On the health app there's a new feature to share your biometric data with your doctor, which I can see improving their accuracy and diagnoses. I'm not sure where you got the idea that the data is garbage, but even I (untrained, not a doctor) can pick up patterns and make positive changes from the data collected.
My comment is focused on data related to mental health issues. A heart rate is a very specific number that is a directly related to your heart function. Cognitive functions, focus and mental health issues can't directly be tied to things like screen use time, sleep patterns, facial expressions, and the most nebulous metric, a self reported mood score.
The point of this research is also to remove the human element from the analysis loop.
