The killer feature of Kodi (on most hardware, for example the Raspberry Pi) is that it can switch the output resolution to match the video you are playing. It also bypasses things like ALSA in order to be able to bit-bang audio in supported formats directly to an external receiver. These are basic functions of normal video playback devices like blu-ray players or cable boxes. A Plasma skin can't do any of this. So wh…
You don't typically don't want to switch output resolution to match the resolution of whatever your outputting on modern displays, but instead want to match the panel resolution and software scale the content. You're way too likely to confuse the monitor trying to match resolution. There's something to be said for matching frame rate, but there's even more dragons in that practically.
I'd also bet with certain types of displays (eg: OLED, HDR and/or local dimming) there's benefits when there's a different aspect ratio (eg 21:9), letting the TV do something different to the backlight when it knows there there is no content in parts of the display vs getting a black signal.