The problem is when "HDR" images that would perfectly fit into the sRGB color space are not rendered correctly on non-HDR systems. This PNGv2 fails that which means it isn't really any more useful and one of the existing (and much better) HDR-supporting formats like JPEG-XL or the video codec based ones pushed by the big guys.
Someone who is aware of this issue can do that. Someone who just uses the standard export might not notice that their files are not backwards compatible. It might also be that most of the image fits into sRGB but a few highlights do not - having the whole image washed out because of those is also not good.
You'll never be able to faithfully represent an HDR image on a non-HDR system, but you'll still see an image.