Are the three progressive thinkers in the late Ming and early Qing dynasties betrayers of traditional Confucianism?

No.

The core ideas of Confucianism are "benevolence" and "propriety". There are also differences in the views of Confucius, Mencius and Xunzi, but they all revolve around the core of benevolence and propriety, so they are all Confucian.

What Huang Zongxi, Gu Yanwu, and Wang Fuzhi opposed was the "totalitarian" monarchy at that time. They had demands for power to be decentralized to small and medium-sized landowners and gentry, but this was still different from modern democratic ideas. .

But they are not against the monarchy, nor are they against the benevolence and propriety promoted by Confucianism. Rather, they vigorously advocated traditional Confucianism, such as the inheritance of the "well field system" concept since Mencius.

This is my personal understanding.