Photo worth a thousand words is below. Summary: Darktable generates a lot of color noise which is really hard to remove in color photography. Why is that? How to fight it?
I just saw the question looking for something else, hence the late date.
According to the Darktable manual (and my experience), the "profiled denoise" works best when used twice: once with "wavelets" and blend mode "colour", once with "non-local mean" and blend mode "lightness". For both, I usually tune down the intensity (NOT blend opacity), until noise gets just visible (preserves details better).
Also, you might want to adjust contrast/exposition, if you really want to compare with the RT image.