Better is a subjective term. In a dark room any OLED would be difficult to beat, but in a bright room a Q90 or any high-end LCD. That is true for HDR and SDR in my opinion.
Yes, I don't see how SDR or HDR matters here. TVs now will map SDR brightless levels to HDR brightness levels. The Q90R seems to do a very good job at this. I agree with your assessment overall. I do love the Q90R's brightness in all situations, though, dark room or bright.