Government does not always mean nation states. In this context I believe it is talking about regional, feudal government for the most part. As for companies, the corporate structure may not have been developed yet, but there were guilds, partnerships and other business ventures. The article does mistakenly use the term corporation in one place, though.

I don't see any contradiction between the linked article and the Wikipedia article. Peasants absolutely benefited from the shortage of labor, while feudal lords lost power. This power vacuum was partially filled by guilds and merchants who were able to take advantage of the new economic situation. I'm not a historian, so I don't know all of the details, but I don't think the two sources contradict each other.

As for historical articles not supporting political proposals, that may be a faux pas in academia, but I would hope that the people making and evaluating political proposals are carefully studying similar periods in history to understand the possible effects of their proposals.