This is a great discussion! To emphasize, corner sharpness is a personal choice. What is acceptable to one person may be unacceptable to another!
A few years ago an amazing image won the underwater category of WPY. It captured an amazing moment, but was shot with a 14-24mm. As a result, the corners were (in my opinion) mush. The judges decided that the moment was worth the award, but all I could think was how much better that moment could have been captured if the photographer understood lens choices!
Typically, wide angle lens designers are not considering close focus ability among their lists of desirable attributes, but it is critical once we install them behind a dome.
The Nikon 14mm (and the 14-24mm), are poor choices for underwater use. Excellent lenses, but simply do not focus closely enough behind a dome port. As @Tom_Kline has pointed out, the Nikon 16-35mm works much better behind a dome port, although even with the corrective lenses and a large dome, its corners start going soft at anything much below f/11 or so. My guess that this is a serendipitous feature of the lens, rather than one that had been deliberately designed.
I must confess that since getting a WACP-1 a few years ago, I rarely shoot with the 16-35mm. This opens up creative opportunities that are unobtainable with any wide angle lens/dome port combination.
Fisheye lenses distort perspective anyway, so even though the aberration is often still there, the curve in the corners seems to hide it. This allows the use of smaller domes. I use a 7" dome with the 8-15mm (and D850) and try to keep it at f/8 or above.
I like thE fisheye effect, but my OCD brain doesn't like it when there are "straight lines" in the image. Silfra does not curve, so my choice would be for a rectilinear lens (or WACP).
Adam