I clearly understanding weakness of Theta X comparing to Theta Z1.
My point only about your definition of “High Quality HDRI” that make Theta users confusing.
Bandai Namco proposed good definition to HDRIs that match scene - “True HDRI”. It not put any label about “Quality”.
And if capture don’t have a goal of exact matching of Backplates and HDRIs but captured HDRI must match scene colors and dynamic range even Theta X can be good. Plus 11K downscaled to 8K even allow to use such HDRIs for reflections or even for background.
I also made a quick and rough test for HDRI with xRite.
result HDRI match scene well, and lightings looks similar to captured moment.
And that’s often what 3D artists want from HDRI 