The people I'm describing as tankies are people I've interacted with myself. I'm sure they don't exist in huge numbers, but they are more concentrated on .ml, they are loud, and they are impossible to converse with. I still like it here because most people here, like yourself, are smart and offering interesting perspectives I haven't explored before.
I agree that the idea of only Eastern propaganda being dangerous and pervasive is wrong. Western propaganda is everywhere too and also dangerous.
One thing that is different is the lack of government-critical sources available from China, also Russia. Freedom of Speech in the West is wobbly, but in China and especially Russia it is even worse (from everything I've read).
This is a lovely segue into our China sidequest, and while I agree on the definition, I have doubts on how public the public sector really is. The way that national election results look and the way vocal dissidents or political opposition are treated does not give me the idea that the people truly have all the power here.
Capitalism concentrates power in the capitalist class. This class can then subvert democracy, resulting in oligarchy. In a similar way, central planning concentrates power in the central government, which actually makes it even easier to abuse that power. Chinese government is not transparent nor federal enough for me to call it democratic or owned by the people.
Your second and third sentence are true. I have definitely seen plenty of shills though.
In my experience I've only seen the word tankie be used by leftists. Libs and conservatives don't even know what a tankie is.