I guess it all depends on what you can tolerate. You say the Pan is 25% better. I bet ausastronomer John would say it's "infinitely" better.
I'm somewhere in between. My 30mm superview in f6 is tolerable, but not very nice to look through. Aberrations are apparent quite close to centre of the FOV and get very bad in the last 30-40%. Panoptic on the other hand...
Even if I had 10 SVs they could not replace one Pan, so is it worth 10x as much? Yep! But clearly, this sort of thing is subjective.
As you are comparing the 27mm Pan and the 20mm SV, I'd say you can see fainter because of the higher magnification, not because of better transmission. The coatings on the Superview are okay, but not as good as on the Panoptic.