Ah...this old Chestnut...
CMOS (read DSLR's) sensors have quite bit more "architecture" over and around their pixels.
This causes diffraction spikes and scattering (image bloat) that are common in even the best DSLR images. (OK, there are now a few Sony back-illuminated exceptions ).
Once you know what to look for these artifacts are a bit like a dunny in a desert.
QE and noise are however are the big killers. When you push the envelope...ie Narrow-band sub-frames of 30-40 minutes..DSLR's simply don't cut it....and it is here, that cooled CCD's become objects of wonder.