Memes

Mostly agreed, though I think south Korea/Corea and north Korea/Corea are valid terms (specifically keeping the cardinal directions lowercase). Capitalizing the direction reinforces the idea that these are separate peoples, but frequently the distinction is necessary when discussing this or that subject, such as the fact that taxation has been abolished in northern Corea. I even more strongly prefer "northern" and "southern" as signifiers.

The problem with using DPRK and ROK alone arises when we are discussing region, not state. The illegitimacy of the ROK as a colonial state set up by the US Empire does not really help us linguistically. The Corean people are one nation, divided. Essentially, I use DPRK/ROK the vast majority of the time, and "northern/southern Korea/Corea" when discussing relational, geographic matters. When discussing the people, I do not distinguish, they are simply "Korean/Corean."

Regarding Japan, it's less a colony and more a vassal state like western Europe. The ROK is more of a direct colony. Japan benefits more directly from imperialism, whereas the ROK is a neocolonial forward operating base for the US to keep China in check.