Good cine glass will outresolve 5k, even wide open. So, your comparisons of frame grabs do not really tell you much.
Most modern 85mm lenses will be very sharp and high contrast (high MTF). Try 14mm.
Not sure what is the point of comparing an antiquated Arri/Zeiss Superspeed lens to a modern Nikon.
It may be just me, but I find still lenses on still cameras a bit limiting in the ability to focus. Probably 90% of time I focus manually when taking stills. I am not sure if this is just economy or weight that influences still picture lens design that makes them difficult to manually focus. I think this is what makes cine lenses on still cameras compelling. It is not for sports or wildlife photography, but for landscapes I think cine lenses have an advantage.
I will be checking the performance of MP14mm against Canon 24mm MK II when I can get my hands on one. What I am interested in is size of the image circle as well as performance on the edges. It may be that MP14 will cover almost FF35, in which case it would be superior choice for night sky photography. But, the 24mm may have superior image circle that will gather more light than the 1/2 stop faster MP14mm, in which case it would be a winner for night time skyscapes.