legal, and also: if you already have been diagnosed, you should already be under medical professional supervision (meds, checkups,…) anyway.

my guess is this is more like the heart irregularities feature: it’s for the first diagnosis. (a relative of mine actually got diagnosed that way)

I believe this is for the fringe cases where you have been diagnosed with hypertension, but your apple Watch does not tell you that you have hypertension risk, then you may decide to not take your drugs, since your watch told you all clear. This could trigger lawsuits if complications set in when you decide not to take your drugs because of "lack of alarm"

Then you get a new fringe case: you are not yet diagnosed with hypertension, but you are aware that your apple watch has that functionality so you decide you don't need to be diagnosed.

It's the same for the Afib detection.

The point of the detection features are to notify people who are not diagnosed with the condition to go to the doctor about it possibly get diagnosed with it.

It's not useful for people already diagnosed because they already know they have it, so the notification is just telling them something they already know.