So I actually purchased a Pico 4 Ultra...
First, it's obvious something was wrong with the colors on Quest 3. I had that impression when comparing to Q2 as well, but became a lot clearer compared to Pico 4 Ultra. On the Q3 i mispressed and found the setting for color space on accident. This was set to rec709. When i changed it to "unmanaged" this helped a lot
But the feeling of depth as a lot better on Pico. Again using scene Sweaty Flexible Desperate for comparison, at about 8:20 when the girls come all up to my face, my heart actually beats noticeably faster when watching in Pico. Nikki moves quite fast forward, and I almost flinch on Pico. That feeling I don't get with Quest 3.
So yeah, seems binocular overlap was the main part of why i had a partially better experience with Quest 2 than Quest 3. And although I have barely had the time to test Pico 4 ultra, for now it seems like a clear winner. I'll try to update after some more use.