HDTVTest evaluates the OT and ST in HDR on Disney+
Vincent of HDTVTest is a respected reviewer and display calibrator. He doesn’t get into color grading or anything like that, but it’s an interesting look into whether the OT on Disney+ is true HDR or just some contrast tweaks (spoiler: it’s not real HDR).
I wonder how much of the issue is “fake HDR.” They may have simply intentionally graded it that way, giving it a restrained HDR pass. It may also be that there isn’t a whole lot of dynamic range to squeeze out of the camera negatives at this point, if there ever was to begin with.
But if I had to guess, I’d say that even if they could have gotten more HDR “pop” they still chose not to, if only so that the OT would still recognizably look like the OT. For all the time they’ve spent keeping the OOT buried, Lucasfilm sure seems to be striving for authenticity as far as the color and contrast goes.