I don't see how 玉 has more etymological significance to 國 than 域/或. What analogy are you drawing on where the previous most common character for land/country is a worse etymological root than a character that apparently has meant only jade (or direct analogies to the material preciousness of jade) for longer than 國 has existed.

As for 黨, it is a direct analogy to 當 as in 當天. There is a little bit lost in the conversion of 田 to 黑 but at least they are related.