To be fair, the 10,000 nit brightness of this monitor is NOT the brightness you can achieve across the whole panel. 10,000 nit measurement is the peak brightness, likely using just a small cluster of pixels while the rest of the panel is black. If you set up a pure white image and cranked the brightness up, you wouldn't get anywhere near 10,000 nits across the entire display.
Where 10,000 nit brightness DOES come into play is specular highlights or similar high brightness but small size objects. The Moon tends to be a common example, think about a very dark scene in a movie at night and the moon comes out in a shot and the inky black sky looks blue/grey because the moon light is so bright that the brightness bleeds into the rest of the scene. With an OLED HDR set there is no more brightness bleeding, the moon is crisp and bright, and the surrounding pixels are dark inky black thanks to the OLEDs infinite contrast ratio.
Tldr; don't let the high brightness fool you, you NEED higher brightness levels in order to achieve HDR, and the better contrast ratio and peak brightness, the better off you are.