Not a doctor, but I was given a diagnosis of severe sleep apnea from an overnight in-lab study. Sought a second opinion who decided it wasn't sleep apnea at all

Not a doctor, but I was given a diagnosis of severe sleep apnea from an overnight in-lab study. Sought a second opinion who decided it wasn't sleep apnea at all. AHI or T-90 are convenient indicators, but pulmonologists will actually look at the shape of your graph and listen to symptoms. All humans are different and don't always conform to formulas. That being said, your observation that a nightly watch user can collect lots of data is an interesting one. If Apple (or whoever) can come up a more heuristic analysis than just computing AHI, they may end up with something better. Also, not that you asked, but my sleep situation is a bit complicated and I actually ended up with a CPAP anyway.