The difference from the AW5 to the 6 is pretty substantial to me. It’s not as big as the 4 from the 3 but pretty big.
I was only able to test both the 5 and the 6 with only three workouts and really thought they were the same. The key differences I see now but unfortunately can’t see true head to head but are obvious to me now. Optical heart is new and improved. It does lock on your heart rate early (unlike previous models and doesn’t let go). Battery life is very much improved even with always on enabled. I did a 2.5 hour bike ride Sunday and after 13 hours still had 52% battery left. Yesterday did 190 minutes of exercise (no gps) and after 14 hours had 57% left. Very similar numbers with battery as I remembered my 3 and 4 series had. Definitely better than the 5. I would had been 20-30% left with the 5. The display is definitely brighter. Especially outdoors. You can turn brightness down half way and get the same with the 5. I was able to test this before shipping off the 5. The GPS seems improved though it has never been annoyance of mine with the watch as others. A few trusted you tubers have tested this and have confirmed this is indeed improved.
My fist 3 Apple watches were inconsistent in recording minutes of exercise. The AW4 was very accurate for recording minutes where my heart rate was above 100. At that time my doctor had my pacemaker set so it wouldn't allow my heart rate to exceed 110. After my Nuclear stress test he allowed my exercise to push to 130 for brief periods of time.
Now I upgrade from the AW4 to the AW6. I agree with your other observations, however I have never seen my green ring register even though my other two rings can circle 1.5 times. Yesterday I monitored my heart rate above 110 for 2 hours. The green ring nothing. This morning, same thing. Yet my wife joined me for about 15 minutes and wearing my old AW4 gets credit for 8 minutes. Me, nothing! Any ideas what is different with the AW6 exercise green ring?
The wash my hands app is also way off on time. Not sure what it's doing to sense the timing but sometimes I can wash for a minute and the timer stops at 8 seconds for 15 seconds then restarts again. The advisory to wash hands when returning home works well. Nice reminder!