Inaccurate tracking of exercise activity and heart rate

I am a physician and have owned an Apple Watch since it was introduced in 2015. It has motivated me to exercise regularly and "close my rings". After the backplate of my 1st generation watch became loose, I replaced it with a Series 2 watch. Something I noted immediately was that my exercise was not being tracked accurately, especially with outdoor walks. The problem has persisted with upgrading to a Series 3 watch.

After talking with an Apple Store "Genius" I replaced my Milanese loop watch band with a Nylon strap with no benefit. I have had long conversations with senior Apple support representatives and sent them numerous Activity App screenshots, to be shared with their engineers. Suggestions (made by the engineers) to wear the watch higher up on the forearm, wear it on the other arm and ask a fellow hiker to wear the watch have not helped. Swinging my arm freely and not using hiking poles and using the "Other" option instead of "Outdoor Walk" have also not made a difference.

I am aware a certain heart rate has to be achieved before the watch recognizes an activity as exercise, and have been told (by the engineers) that having achieved that rate, the target rate has to increase with subsequent exercise sessions before the watch "credits" the effort as exercise. The latter statement is physiologically illogical. As one exercises regularly and becomes physically fit, the heart rate during exercise of the same intensity becomes lower.

Two other problems I have noticed are:
1. Periods when the watch does not track the heart rate - "black holes" during work outs. Looking back at the data from 2015 these instances of missed heart rate tracking were infrequent.This happened very often with the Series 2 Apple Watch and is less with the Series 3 Watch (although still more frequently than with the original Apple Watch).

2. Inaccurate recording of the heart rate - Just this morning, while briskly on a trail with a gradual ascent, my heart rate was recorded as increasing from 108 to 133 beats/minute and a couple of minutes later dropping to 81 beats/minute. Later, I had several reading in the 60's. I have periodically manually counted my pulse rate during the hike and it has ranged between 104 and 120 beats/minute.

I wonder if the accuracy of the watch's heart rate sensor has changed or if software updates are affecting tracking of the heart rate. Either way, since Apple wants to promote the Apple Watch as a health care device the accuracy of data that it records needs to be validated. I am a participant in the Apple Heart study and till date (88 days) have contributed 365 samples of "heart rhythm data" to the study. I presume this is recording of heart rate rather than rhythm, since my heart rhythm is regular (I do not have atrial fibrillation or any other rhythm disturbances). I called the study contact number to try to talk to a medical professional involved with the study a couple of months ago, but am yet to hear back.

I would appreciate comments from other Apple Watch users who might have similar observations and learn if they have been able to devise any workarounds.