Well, I think a couple things need to be considered here:

First, the conditions in Korea and Cuba are unlike those in the imperial core in that they come from backgrounds of historically underdeveloped capitalism and have had their growth stymied greatly by economic sanctions. Liberal reforms are an extemely useful way for these countries to build up the productive forces that Marx assumed would already exist when proletarian revolutions occurred. An agrarian society, one coming just out of feudalism, can't develop straight into a more advanced form of socialism just because socialism is such a good idea; the forces of production must be sufficiently developed first.

The circumstances would obviously be different in a developed, fully industrialized nation like the US or UK, but again this would be due to the differing material conditions, not the ruling parties of these socialist countries just not doing socialism right.

I also haven't read anything about the DPRK liberalizing their economy recently.

Second, features that are shared in common with capitalist production will inevitably exist under socialism as part of the process of building communism. For example, commodity production exists under socialism and will exist in every socialist country basically until world socialism exists. It can't just be willed out of existince, at the very least because trade is necessary and global trade currently exists under conditions of global capitalism; to acquire needed goods on the market, goods have to be produced for sale on the market in exchange. But also, again because of historical underdevelopment, many socialist countries maintain internal markets, such as the farmers' markets in the DPRK, in the absence of more efficient forms of central planning that aren't yet possible.

But regardless, these workers aren't proletarian since they aren't employed by capitalists who appropriate the value they produce.

As far as classifying countries as good or bad, I think it's reasonable, as socialists, to classify those countries that act against the interests of the global proletariat as bad, and those who act in their interests as good; imperialists bad, anti-imperialists good. Rooting for socialist countries is internationalism.