There is no argument here really , I did not come to that verdict out of speculation.
We know that the most important factor to consider for TV's picture quality is the contrast rating , which is the measurement from the brightest part to the darkest part of the screen .
The whole purpose of local dimming was to enhance these aspects . Therefore making the brightest part brighter , darkest part darker , directly contribute to the increase of contrast numbers .
There are 2 types of local dimming system in the TV market right now :
The FALD . In a typical fashion , FALD is able to divide the whole backlight system into multiple zones of lights , darkening selected zones while boost white of the brighter portion.
Which is also why , TV with more zones is usually has much higher contrast ratio when Local Dimming is on .
Obviously the GX800 does not fall into this category so we will stop talking about this .
Moving on , we have the second type of local dimming which is edge-lit , like what you saw on NU8000 .
Due to its nature of being edge-lit , these TV can only improve on boosting the brightness because it lacks the more advance zones to shelter the backlight completely [ due to it lighting up the pixels from the edge of the screen].
The cons being , when it lights up the screen it usually brighten up the entire column , hence doesn't improve the dynamic range as well as the FALD .
You are correct in a sense that we already have a great example of it which is the NU8000 .
Being an edge-lit local dimming TV , it is able to shoot past 800 nits . That is a whole lot of headroom for HDR compare to GX800 .
If we go by your logic , the GX800 should belong to this category assuming it does really has a local dimming .
Now back to the question , where is the benefit of having this type of local dimming system ?
The sole advantage of being an edge-lit L.D is you still get a pretty good boost on the luminance like the NU8000.
Merely having a peak brightness of 300 cd/m2 , the sole benefit of edge-lit Local Dimming is almost non-existent . It is definitely not an FALD therefore the enhancement of having deeper black levels have vanished as well .
It doesn't boost its white or black levels , therefore bringing nothing on the table on the perspective of picture quality .
To be fair the TV is still fairly decent for having WCG and good accuracy OOTB but those benefits has nothing to do with its local dimming system .
The same exact Malaysian GX800 is in Germany as well. (IPS, edge lit)
I have seen some measurement number of this TV before, for HDR it goes nearly 570nits.
End of the day it is all about user experience. I like GX800 PQ way more better than NU8000. Most of my family members agree too.