Hard to say. The far left tree is soft to me, but it looks much like my X4S does without a filter.
My X4S images at the sides of the frame are soft normally as the optics aren't as good as on the X5S. The way you have put the Polar Pros at the edges might not be a good test if your camera is soft as is mine, and then placing the Neewer in the sharper middle portion. Maybe three images of the same shot, one with each of the two filters, and one without any filter would show better.
Also, to rule out a tilted sensor, try and set up a shot perpendicular to some chain link fence and turn on the focus peaking to high and see if the red edges appear equal on the fence edges on both sides of the frame. If one side is more red, chances are your sensor isn't parallel to the bayonet so any sharpens tests of filters will not be worthwhile. My X5S was bad enough that when I turned the focus wheel in MF, the red would move across the target (fence) indicating it was misaligned from the factory. It should all go red at the same time.
