Albatroz,
You say we should be concerned with real scene peak brightness, and that's exactly why I look at the 10% and 2% patterns. I've watched a lot of HDR video, and in general it seems only highlights that have extreme brightness. Things like a flashlight or headlights, or the sun reflecting off waves in a stream, neon letters, etc. Those only take a small portion of the screen at any one time. I don't recall too many times that a large portion of the screen went to really high brightness. Not to say it never happens, but for me I mostly concern myself with 2% and 10% window readings.
I do agree that having an HDR TV capable of at least 1000 nits will provide the best experience. If you look at metadata on HDR streams, most are either mastered at 1000 nits or 4000 nits. If it's mastered at 1000 nits then no tone mapping is involved. Even with 4000 nit mastered media the peak brightness doesn't often go over 1000 nits anyway - at least in the ones I've looked at.
I can't comment on how good the implementation of HDR is on the mu series since I haven't spent any amount of time evaluating it. I can say that on the KS series, with well done HDR, it's a nice improvement over SDR.
As for getting a better HDR picture, I'd try this first as a test. Make your room as dark as possible, or wait till late in the evening and keep all lights off. Turn your SDR backlight down to 6 or 7, then switch back and forth between an SDR movie and an HDR movie. Try and get the average brightness to be about the same, lowering or raising the SDR backlight as needed. How does the HDR picture look compared to SDR with the backlight adjusted? Try a couple different HDR movies. If HDR doesn't look as good as SDR when the brightness is matched, it's possible you may need to adjust your HDR settings.
You could try Dynamic Contrast set to Med or High, or you could try setting the Gamma to 1. If you set it higher you could get more brightness but at the expense of washing out the picture. See if any of that works for you.