Main thing I see is some smoothing, no real color change.
You might want to look into QTGMCs custom options, especially the 'Lossless' option.
Cu Selur
Had to dedicate some time elsewhere last week. However I've spent some time on this and seems to the antialias was causing a lot of the banding, dfftest was also a lesser culprit however changing to mctemporaldenoise seemed to gleam better results. I'm assuming its still down to the video being picked up as 8 bit in hybrid but not sure on this one.
Check the "Vapoursynth Script Preview" it should show how the video is processed.
Cu Selur