Players can already adjust the contrast and visibility of things on screen as has been said. Monitors sharpen the image, control saturation, contrast. Digital vibrance, anisotropic filtering, gamma adjustments, ambient occlusion settings, even dynamic super resolution smoothness settings in driver control panels greatly change the way the game looks. None of it is “cheating”. They’re all benefits of using PCs, much to the disdain of console plebs 
If anything, Freestyle users would put themselves at a disadvantage compared to those not using it. If I want to limit my visibility by using depth of field and blur for a prettier effect, why not. There aren’t any filters that render distant objects any sooner compared to using no filters, or any magnification.