It is a decent monitor (native 1440p support ) but you are not going to get good HDR experience from it .
Also the 43" and 49 " are restricted to only 60hz refresh rate and no VRR supports which is disappointing.

It simply can't get bright enough to deliver the HDR impact .

That is correct .
For the best results , LCD needs to have 1000 nits + and have Full Array type of Local Dimming System to showcase the "Wow" effects ,  500-600 nits for OLED because they have infinite contrast .
LCD TV with 500-600 nits are still significantly brighter than traditional display , so the HDR effects may not be impressive but it is still very obvious.
There are a couple of outstanding mid-range TVs in MY like the good old NU8000 , Q6FN etc etc .
These are generally considered as "basic level HDR experience " , suppose to give you a taste of HDR without breaking your piggy bank .
They have the brightness but not the contrast .

Samsung's Q75R which was just released early this year is also a good HDR display with Full array dimming and Quantom Dots filter but it is still very expensive .

If you are just looking for HDR monitor  , I would recommend you get the Philips Momentum model no 436M6VBPAB which has a brightness of 1000+- nits and is much cheaper than the other HDR monitors ,  it only available at 60hz refresh rate though and I wouldn't use it as TV because of the poor viewing angles .

Probably RU7400 since they covers a wider color space than RU7100 . While the brightness are lacking , you should still at least get more saturated colors from HDR movies and games .

The native 1440p support is great too incase you need to switch to lower resolution .