I've read about the lamp mode switching to high/normal also when using HDR since HDR requires more brightness.
But now I have confirmed this 100%. The PJ switches back and forth from Eco to Normal to Eco when color setting switches back and forth from SDR to HDR to SDR.
Again, the HDR pass-through looks awesome.
But then when I switch back to the Plex desktop, the HDR->SDR tone mapping done by Plex looks just as good to my naked eyes even though the HDR is Normal Lamp mode and the SDR is Eco Lamp mode.
It sounds very weird, but if Plex Tone Mapping looks just as good as HDR Pass-through plus I don't have to put up with the 4-second HDR-switching-pause black screen nor the Lamp mode switching from Eco to Normal, I think I'm going to just use the Plex desktop.
It sounds strange not to care about HDR Pass-through, but oh well.
I also prefer the looks and feel of my HTPC much better than Shield TV.
But yeah, like you said, it's personal preference.