Generally the abberations should scale somewhat linearly. Jon suggested the 16 UWA might not be as linear and might hold up better at mid F ratios before tanking more at F4, hard to say. Unlike Jon I don’t get cheap eyepieces that can’t compete with what I (or even my kid) already own just to report out to others so I can’t say from personal experience. Do keep in mind that Jon was using a coma corrector that costs about as much as an 8” Dob, and generally wouldn’t be considered needed at F6, and the coma corrector has a reputation for reducing the effects of field curvature. So his experience with the 16 UWA might not line up with yours, although he was operating at F5 not F6. Personally I am picky about edge correction so I will just avoid eyepieces known for bad edge correction. I could care less about EOFB. You just have to understand your preference.
Jon is right that you can tame the tield curvature a bit by shifting the focus slightly. You give up a little contrast in the center but the edge performance improves. So you can make a wider view look decent at least. Ernest’s bench tests showed the 16 UWA besting the Nagler in the center so clearly there wasn’t any effort made to balance the focus and improve edge correction. Also to some extent the eye/brain can accommodate some degree of FC, which could contribute to the opinions on the 16 UWA generally ranging from it’s decent to its just plain bad.
I can be extremely picky about edge correction and arguably own the sharpest eyepieces manufactured. I also own and use the best coma corrector available as well as a refractor that is fully corrected for field curvature as well as the other aberrations. My eyes are free of astigmatism even at large exit pupils so I am pretty confident in what I see as the eyepiece's aberrations.
A coma corrector does not corrector coma in the eyepiece nor does it correct field curvature in the eyepiece. What it does do is correct the coma and field curvature of the mirror so the field curvature and coma seen in the eyepiece are those of the eyepiece and not the mirror or objective, in the case of a field flattener.
I do not consider $100 "cheap" and I buy eyepieces like the 16 mm UWA to use. In the case of the 16 mm UWA, I traded a finder for a new eyepiece shipped from Astronomics. My hope was to use it in my 50 mm F/4 StellarVue finder as the finder's eyepiece. It would have provided something like a 6.3° field at 12.5 x. Unfortunately, the barrel is too long so it won't come to focus.
It does focus in my 50 mm F/5 Astro-Tech finder and would provide a 5.0° field at 16x, so if I can figure out how to install cross hairs, it still maybe still viable. I did try it and it's actually quite nice though I did not give it the full test.
When I discuss an eyepiece, I like to have some actual experience with it. I don't discuss Delos and Delites or Morpheus's because I have no experience with them. People are spending money on eyepieces based on what they read here so I want to be confident in what I'm posting.
Relying on the numbers only gets you so far and as Tangerman discovered, the numbers for the UWAN are significantly better than the numbers you found ,
Your numbers: 16 UWA: under 2, 38, 72
Tangerman : 16 mm UWA: 16 UWAN: 4, 20, and 55.
Those make much more sense to me. The very edge is not so pretty but in an 82° eyepiece, it's not staring you in the face the way it is with a 65° eyepiece. The rest of the field is pretty good.
I believe that if you'd ever actually looked through a 30 mm GSO Superview as well as a 16 mm UWA, you never would have suggested they were similar. Likewise with the Expanse eyepieces, this eyepiece seems better than the 9 mm Expanse by quite a bit.