You're wrong in that thread too. Typically of the DxO bashers, your MO seems to be repeating the same falsehoods and hoping noone calls you on it.
Typical of the DxO defenders, your MO is name calling and begging the question and hoping no one calls you on it.
If you think the images truly do have the same dynamic range before and after you downsample, you need to normalize.
No, you need to perform the test and show us the results. That will put an end to this bickering.
The downsampled image will have less noise, therefore a lower blackpoint, and therefore more dynamic range on a per pixel basis even though it doesn't have more of what you'd intuitively think of as dynamic range.
I don't give a pile of used dog food about your white point - black point definition of DR. I'm not trying to make my blacks blacker. I can do that with NR and levels adjustments. I care about real, usable photographic detail. Down sampling and 'normalization' does not magically create new detail.