If I wanted to use my Apple Watch in low power mode and disable all the features I paid for I’d rather just buy a Garmin. My series 7 with AOD enabled and a 1h workout barely lasts the day (10% remaining usually). If I turn off all the features I can get 2 days battery but as I said then what’s the point?

Try disable low power mode, enable AOD do some workouts, be active and use your watch throughout the day and I’m pretty sure your ultra will be at around 50%. That’s a more realistic use case.