The first thing that occurs to me is, maybe you can create a texture mask in Gimp or Photoshop to lay over that harsh line and tone it down. You can always try and fiddle around with the color ramp, but I guess that’s where you’d loose detail. You can also modify that same texture that is giving you the harsh line, put some neutral gray over the line to tone it down or get rid of it entirely. You don’t have to go to Photoshop or Gimp by the way, you can do it inside of Blender with texture paint. And in case you want to go back, maybe do a Save As of the texture before modifying it. Hope that helps.
