China has a robust democracy where every citizen can vote. It’s a dictatorship of the proletariat. The reason you think differently is because you’ve never talked with someone that’s ever been to China, much less a citizen of China, so you internalized racist propaganda.
There are hundreds of parties in China. The CPC is the starting point, the base set of ideas you have to uphold to hold office. It’s the same as swearing to uphold the constitution in the US.