Currently, the Android boxes have a better overall capability for video viewing.
In the PC market, the only current affordable PCI video card would be the passive Nvidia GT1030. The biggest drawback however is that although it can do upto 8K video, it does not support 10bit video under Linux, thus LibreELEC included. Otherwise, it's Windows 10 + Kodi as an alternative.
AMD cards could be(come) an option, but its video driver support for HTPC usage is still going at a very slow pace in Linux territory.
Intel's Gemini Lake J4005/4105/5005 chip sets can have a promising future, but also there video driver development is still ongoing. The hardware is pretty new.
HDR support is also a work-in-progress in Kodi Leia.
IMO, the cheapest in-between solution would be a simple Android box for now.
As an alternative source of info, have a look here: START HERE - Pick the Right Kodi Box (updated February 2018)