Wouldn't this be contradictory to historical materialism?
Not really. The point is that no ideological alternatives could gain any traction in Chinese society for more than two millennia precisely because of the economic basis of ancient Chinese society. If the economic basis of society is rapidly changing on a time scale of years rather than centuries, then people will be more prepared to think radical thoughts or to come up with new ideas - as Lenin put it, "one must be as radical as reality itself". Britain in the 19th century is a good example of this. And modern China is, in fact, a good example of the point which Engels emphasised - that the base-superstructure relationship is not mechanistic but dialectical
- that is, it is a reciprocal relationship in which, in the first instance, the base determines the superstructure, but (as a second-order effect) the superstructure also determines the base. If there is a distinct lack of ideological alternatives to the existing system, if the political rulers of society actively suppress any and all dissenting voices, then this will make changes to the base difficult or even impossible and may delay economic or social progress for decades or even centuries. Tsarist Russia in the 18th and 19th centuries, or late imperial China, are good examples of this.
Since the late 19th century and certainly in the second half of the 20th century, China - either in its state socialist or state capitalist form - has brought about a transformation of social classes, with the demise of land-owning gentry class, the growth of an enormous working class, and the emergence of a middle class and capitalist class that are both so far more dependent on the state than vice versa. In other words, there is a rather archaic state structure trying to manage a capitalist class structure, leading to a lot of state-society tensions and instabilities. Whether people have some alternatives in their mind or not are important but secondary to the material conflicts.
But people having alternatives in their mind is an important component of achieving a successful revolutionising of the material base. China suffered a century of humiliation precisely because nobody in China had the slightest idea of how to counter the new threat from the West, nor did they even conceive that China would have to revolutionise its material base and its political system, which had lasted for more than two millennia and was firmly believed to be part of the natural order of things. No ideas, no revolution. After all, why did Marx bother to write Das Kapital
or the Communist Manifesto
if he didn't believe that it matters
what ideas people have in their heads?
"Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies." - Marx (Groucho)