The difference you see is probably due to different post processing presets, you could probably tune kodi to look better but in general it was designed originally for very low power devices and never added a lot of enhancement functionality outside of a few plugins for it. Try using the older kodi+dsplayer version for more tweakability or look I to madvr for massive image enhancement capabilities
The only reason I have kodi installed on my main nvidia shield is because it’s the only player ive found that will play back surround and atmos audio files (multichannel Flac and Atmos M4A) without then having to be in video containers. So it works well for my surround hifi rig.