There are only really a few places the Apple Watch helps for photography:
Planning. It's nice being able to see sunrise/sunset times at a glance, as well as weather forecasts. Unfortunately PhotoPills doesn't have a Watch app, so you can't really add any complications from that. The Watch does at least have moon phase as well.
Camera Remote. The stock Apple camera app supports this, as do most 3rd party ones (ProCam, Halide, etc). This is nicer than a traditional remote because you can see the screen if you're trying to get in the shot far away, or looking away from the camera.
Recording hikes/runs/biking. This is probably the only category the Ultra will shine over the Series 6. I like to record all of my activities, and Lightroom even supports importing the recorded track to geotag photos taken with a camera that doesn't have GPS. If you find yourself running out of battery with the current watch on a hike and you use other Watch apps regularly, that's what the Ultra is for. If you find yourself running out of battery but don't really use many other Watch apps, I would probably check out Garmin because they make better fitness/outdoors focused watches.
Personally I have both a Garmin Fenix 5 and an Apple Watch Series 6. I switch back and forth depending on the activity I'm doing. The Apple Watch wasn't good enough at tracking runs/hikes, and the Garmin isn't as nice the rest of the day (I don't know if the newer ones are better, but my relatively old Fenix has a very harsh vibration motor). I'm hoping the Apple Watch Ultra is a good compromise between the two so I don't have to go back and forth between two watches. It would be nice to have all my health data in one place! The one advantage of the two watch solution is one is always on the charger!
