“In this case I optimized the display for HDR content in general, which always appeared somewhat dark, flat, and desaturated on my TV screen, compared to SDR content even if the dynamic range was obviously increased.”
The problem is that most people have their TVs set with very high SDR brightness levels.
At least for me the recommended SDR brightness of 100 to 200 nits (according to sources, most mention 100) is just too dark…
So yes, HDR will look dark in comparison, but that’s how it was mastered…