To spot some differences one could look at the lightness histograms of the grain for 10%, 50% and 90% gray.
The darktable grain at 100% intensity has the following histograms.
The 10% and 90% histograms look a lot narrower. I wonder if it would be nice to tweak them so that they match your grain @Carmelo_DrRaw
, which is more sophisticated.
It performs essentially in the same way since it is only a tweak of the weights and frequencies of the noise octaves.
Here are the power spectra trends.
For direct comparison here is the old implementation.