I find this reply very strange because it's the core point of Marxism that it's dialectical but materialist. It has a lot of forebears, but Hegel is the most direct and obvious of them.

This new German philosophy culminated in the Hegelian system. In this system — and herein is its great merit — for the first time the whole world, natural, historical, intellectual, is represented as a process — i.e., as in constant motion, change, transformation, development; and the attempt is made to trace out the internal connection that makes a continuous whole of all this movement and development. From this point of view, the history of mankind no longer appeared as a wild whirl of senseless deeds of violence, all equally condemnable at the judgment seat of mature philosophic reason and which are best forgotten as quickly as possible, but as the process of evolution of man himself. It was now the task of the intellect to follow the gradual march of this process through all its devious ways, and to trace out the inner law running through all its apparently accidental phenomena.

That the Hegelian system did not solve the problem it propounded is here immaterial. Its epoch-making merit was that it propounded the problem. This problem is one that no single individual will ever be able to solve. Although Hegel was — with Saint-Simon — the most encyclopaedic mind of his time, yet he was limited, first, by the necessary limited extent of his own knowledge and, second, by the limited extent and depth of the knowledge and conceptions of his age. To these limits, a third must be added; Hegel was an idealist. To him, the thoughts within his brain were not the more or less abstract pictures of actual things and processes, but, conversely, things and their evolution were only the realized pictures of the "Idea", existing somewhere from eternity before the world was. This way of thinking turned everything upside down, and completely reversed the actual connection of things in the world. Correctly and ingeniously as many groups of facts were grasped by Hegel, yet, for the reasons just given, there is much that is botched, artificial, labored, in a word, wrong in point of detail. The Hegelian system, in itself, was a colossal miscarriage — but it was also the last of its kind.

It was suffering, in fact, from an internal and incurable contradiction. Upon the one hand, its essential proposition was the conception that human history is a process of evolution, which, by its very nature, cannot find its intellectual final term in the discovery of any so-called absolute truth. But, on the other hand, it laid claim to being the very essence of this absolute truth. A system of natural and historical knowledge, embracing everything, and final for all time, is a contradiction to the fundamental law of dialectic reasoning.

-- Engels, Socialism: Utopian and Scientific

i don’t think social change boils down to just one theory.

If we believe that the universe fundamentally makes sense, then it must stem from that that it can all be explained on the same terms. Furthermore, within a domain, the extent to which a theory is unable to explain some part of that domain is the extent to which it either fails or is in-utero just a component of a larger theory whose other parts can cover those other areas. Not only can social change boil down to one theory, if you believe we live in an interconnected, logical world, it must boil down to one theory. Obviously there are many competitors for that title, and none of them are yet developed enough to properly claim it, but it is a legitimate and even a necessary title.

Edit: Sorry for piling on about the dialectics part, I see Cowbee did go over it later. fwiw I think he didn't represent materialism fairly, but part of why I included the Engels quote is because I think he does represent Hegelian idealism and its fundamental problem (How can this dialectic of humans -- material beings -- take place in the world of ideas?) fairly.

Idealism is wrong, though, so focusing on it is useless IMO.