[FoxADRIANO]

It's worth remembering that Shield TV is sold primarily as a gaming platform, with Netflix and Amazon Prime Media player duties as a strong secondary use case.  In that arena it's a pretty good choice.  

nVidia don't really have any significant interest in Kodi - though as a 'background' driver for sales, and I suspect because some of their developers may also run Kodi personally, it does get some support.

If you compare the Shield TV to its nearest rival - the Apple TV 4K - both have pluses and minuses.  There is no perfect box.

Also your use case, which is UHD Rec 709 SDR, is incredibly niche.  TVs and Media Players are not hugely concerned to correctly support content in that format as it's not in widespread commercial use.  I'm not saying that excuses poor support for that format - but it is not going to be something that gets a lot of effort targeted at it. (Heck - my previous Sony UHD HDR TV couldn't display native 50Hz content without dropping and repeating frame pairs in anything other than GAME mode...)

UHD HDR10 Rec 2020 is the dominant UHD format (along with DolbyVision), with UHD SDR Rec2020 the secondary UHD format.  UHD SDR Rec 709 is not in widespread use by any major production on Netflix, Amazon Prime, BBC etc. 

I don't know why every time you answer to my posts you are able to calm down. I know, you already told me other times all that you have just written. What I regret is that a good device to watch video files doesn't exist. You tell correctly when you tell UHD is HDR10 Rec 2020 but there aren't cameras or videocameras with that option. All cameras are Rec 709.  I don't refer to broadcast cameras with a prohibitive cost for us mortals. I refer to semipro cameras. Now I have Lumix GH5 and it is considered the best camera in the world for video but there isn't UHD HDR10 Rec 2020. I don't know what to do. ufff