Originally Posted by microwiz
No it darkens the entire picture, you wouldn't have to bring back mid tone and "normal" highlights if they weren't being reduced in the first place.
There are some slightly perverse arguments you can get into around this.
No one is watching HDR content on projectors in "Panel Gamma" - everything is tone mapped, the question is what is the map.
Some thoughts to mess with your thought process and mojo:
1) HDR is not High Brightness, but High Dynamic Range. Black to midtone is just as important as midtone to specular highlights (arguably more important).
2) If all you did is have extra brightness from leaving the filter off, your peak white has improved but contrast has actually stayed the same. But your native black level has worsened.
3) Now, if you have two maps that put the bulk of the midtone of the dynamic range in more-or-less the same luminance range, you've actually given yourself improved dynamic range between black and the midtone in the case with the filter in place and lower peak brightness, and improved contrast between the midtone and black. Albeit at the cost of some of the top end of the dynamic range at the very top (specular highlights)... But you can't have all the specular highlights described anyway. You are already MILES away from what those specular highights should be. I mean, a highlight which should be 1000nits is, for example, 164nits instead of 200nits. (20% vs 16.4% of target). Doesn't sound like a lot in those terms. For a 10000 nit title it is even bigger.
4) In putting the filter in place you're also representing the black - midtone area of the dynamic range with more of the panel gamma, so you have improved colour resolution between the midtone and black.
It's just not as clearcut as more peak brightness is the best HDR image.