The difference is negligible, and the Ultra 2 still has watch faces that show more information on the screen.
Overall, I have seen people claim that the Series 10 is somehow more technologically advanced than the Ultra. It’s not, the watches are effectively the same after the update to WatchOS 11. Ultra 2 has speakers, sleep apnea detection, bright screen, strong battery life, etc. The screen size is effectively the same. The Series 10 does have the better viewing angles, but that is a very small thing.