Yeah colors outside of HDR are actually much improved... before in PC input prior to the patch, the set was pushing a ton of cyan, due to wrong gamut tracking. No surprise that Mario looks better now!
I hope it just isn't my set, but HDR is completely messed up in PC input for me. Everything is dimmed and colors seem to have been layered in black overwash, completely dulling everything.
Is there a reason to use PC input for HDR? Outside of convenience, I mean. Switching the input icon every time is a little annoying of course.
That said, I just played Wipeout in HDR and the TV lost the picture signal twice in about one hour, which didn't happen once in 40 hours of Horizon on the old firmware. So I would second what you said: don't update yet if you use the TV for HDR gaming.