I don't have the articles from 2018 but there were numerous reports that the Apple Watch (and others) were inaccurate for heart rates. I can tell you from experience that numerous Fitbits are terrible at counting steps (which is why I bought it in the first place back in 2016) and that's their sole function.
Again, I welcome and dream of a day when such a medical device can be used, is trusted, and is accurate. We are still in the beginning stages of such technology. But accuracy is critical. Responsibility is even more critical. All of the numerous devices found in hospitals are vehemently designed, tested, and repeatedly tested and maintained to ensure accuracy. When those devices fail and a lawsuit comes, it's never the hospital that is liable...it's the manufacturer. This liability needs to apply to said Apple Watch-type devices in the future. Apple can't simply shrug their shoulders and say "well, I guess the Watch didn't work that well that day...but our TOU says we can't be held liable" if the Watch fails to work as promised for medical usage.
Surely there's a difference in usage. Apple's devices are specifically for personal information rather than for use by medical practitioners. I don't see a doctor/hospital using an Apple Watch for accurate diagnosis (especially in the USA), but I can see it alerting them to a possible problem that can then be checked (or enable them to focus resources away from unlikely issues). While improved accuracy is always good, there's a lot of benefit in broadening access to diagnostic healthcare devices as long as the user is aware of the limitations. Early detection and seeking medical attention can be critical.
In my home, I have many cheap DIY devices to test for damp, detect electrical circuits, measure temperatures remotely, test electrical continuity, check for water leaks, etc. as well as checking my heart rate when exercising etc. They certainly aren't good enough for professional use, but they do help me detect and correct problems before I need the professionals, tell me that I need to call someone in before the problem becomes too serious, or enable me to monitor ongoing issues. Most of them have similar caveats to the Apple Watch.