Corrner performance is down to physics for a given lens focal length all else being equal. The corners are unsharp as the lens is trying to bring a curved virtual image into focus while the lenses are designed to bring a straight line into focus. As the corners are physically closer they fall outside the plane of sharp focus and end up rendering soft. A larger dome places the virtual image further away and the difference in distance between centre and edge is closer to falling in the plane of sharp focus. On top of this you need to stop down enough to increase depth of field bring everything into focus.
Agree with Adam f8 is not enough with any dome to bring everything into focus. An 180mm dome is also too small even stopped down to get good corners.
This link has shot taken with a 17mm lens shot at f8 on full frame with a 170mm dome. The 14mm will be significantly worse :https://uwaterphoto.com/?p=839
This is why fisheye lenses are popular underwater as they are not constrained by bringing a curved virtual image into focus and they will work at slightly more moderate apertures with smaller domes than rectilinear lenses in a dome and be sharp to the edge of frame.
If you don't like fisheyes perhaps WACP might be a better option, somewhat expensive as Nikon does not have a suitable lens to use with the WWL, but certainly superior results to a rectilinear lens in a dome.
The 14-30mm f4 takes 82mm filters so you could use the S&S correction lens with it to improve your corners, it is available in 77 and 82mm filter sizes. I believe it is discontinued so you would be looking for a second hand one or there may be some stock out in stores. You would still want to use this with a 230mm dome.