I appreciate you agreeing with my assertion that an Apple Watch user needs to be tethered to the power socket multiple times a day, even if it’s for 10-15 minutes at a time.Changing pixel density alone is not going to quadruple battery life. The main drains for the battery are: the CPU, the radios, and the LEDs for heart rate.
Apple Watches are true activity trackers for what 99.99% of what people do, and I suspect that they would work fine (from a battery life perspective) 80%-90% of the time even for extreme athletes. Even with two hours of GPS and stats tracked walking/jogging, and one-two hours of indoor workout, I get through 24 hours of use with a 15-20 minute charge during my shower when come back from my two hours in the morning and 15-20 minutes when I get ready for bed. With the Apple Watch Ultra, I might be able to get with nothing more than that, even on the days when I use the watch completely standalone when I am on the track.