The assumptions given by mechanical materialism are incorrect, though:

1. That the world consists of permanent and stable things or particles, with definite, fixed properties;

2. That the particles of matter are by nature inert and no change ever happens except by the action of some external cause;

3. That all motion, all change can be reduced to the mechanical interaction of the separate particles of matter;

4. That each particle has its own fixed nature independent of everything else, and that the relationships between separate things are merely external relationships.

Each of these assumptions, seeing the world as a purely mechanical system where development is impossible points us to absurdity. I'm sure the mechanical materialists would disagree with the idea that development is impossible, but this is the necessary conclusion of mechanical materialism's basis. It's why dialectics is a necessary advancement.

Since dialectical materialism is meant to be predictive, doesn't that make it falsifiable?

Well, the systems theory exists in part because of the cryptic philosophical traditions, and understanding the cryptic philosophical traditions allows us to recognize when someone is attempting to develop the supposed next best thing after systems theory and they just end up retreading old ground (as liberals so often do).

As well, systems theory doesn't really do much to explain how and why philosphical ideas themselves change.

My point is that systems theory is dialectical materialism. Marx didn't invent dialectical materialism. Legalists during the Zhou dynasty were already using dialectical materialism. It's the main reason why the state of Qin was able to steamroll the other Chinese polities and unify China despite starting out as an incredibly weak state because their main ideological competitors were a bunch of Confucians, Daoists, and Mohists, none of which espouse a dialectical and materialist framework (with the Mohists being neither dialectical or materialist).

Of course, their version of dialectical materialism is cruder than what Marx came up with. Systems theory is just the latest iteration of dialectical materialism. So why call Marx a dialectical materialist instead of retroactively calling him a systems theorist? Well, it goes back to what I said earlier about systems theory being an exercise in branding from anticommunist Western scientists. If anything, systems theory should be rebranded as dialectical materialism. Systems engineering should be renamed to dialectical engineering and so on.

Well, I agree with the analysis you laid out and I'll gladly admit, it subjectively seems "good" enough for me as it is without explicitly referring to either dialectics in general or specifically dialectical materialism (which is not as broad and difficult as dialectics in general, which I don't claim to be necessary).

However what does "good" or "better" mean exactly? We know it's a good analysis, because it's compatible with the principles of historical materialism. It looks at classes, it takes into account that society has to reproduce itself, it conceives of the world as ever changing rather than static and most of all, aims to change it in the right direction. So why is historical materialism good for producing analysis that is able to change the world? You can't say it's good because it produces good analysis, that would be circular. Why can we rely on historical materialism to produce good analysis? Maybe another method would provide even "better" ones? How did it's inventors arrive at it? By applying the more general philosophy of dialectical materialism to human history.

Why simple things like: "actual change in the world matters more than ideas about it", "contradictions drive the development of things", "things are defined by opposing principles", "gradual change turns into real difference suddenly" are true, is explained by dialectical materialism and that's what historical materialism is build on.

We don't all have to get into it, it's enough if some intellectuals keep it alive. But where it is forgotten completely, mistakes are made. A good example of a wrong analysis, that claims a vulgar materialism but lacks dialectics is the gender essentialism of terfs.

If one does not deploy dialectics, one can essentially argue that Russia went from a massive empire with a monarch, to an even larger empire with a dictatorship (the liberal understanding of history).

While instead Russia can be understood as a series of internal contradictory processes, such as the pursuit of modernization (an idea) without the state, bureaucratic or educational institutions to support that pursuit, for example (the material). A potential negation of this is communism. However, it isn't that simple, and with the external pressure applied, the negation of the negation could potentially look a lot like what Russia under the USSR looked like, with it's own internal contradictions. A socialist state under the same geopolitical pressures as Imperial Russia.

Basically, the USSR may have somewhat resembled Imperial Russia, but we know that it only looks like that because of the negation of the negation. We could also use materialist or systemic explanations, however, only watching the material angle allows the changes to be obscured.

Dialectics helps us understand and analyse the outcomes of historical decisions, as well as helping us analyse the potential outcomes of current decision making. It has an important focus on internal contradictions of a thing, which can help us understand why the class composition of the USSR led to particular historical outcomes besides the looming threat of nazism. It can also help us better analyse the components that resulted in the break down of Soviet socialism, the economic and social factors that led to the break down and why those formed intrinsic parts of the Soviet model. They were not imposed on it from without, they were historical conditions that required navigating by the communists at the time. Without dialectics we can miss the forest for the trees and avoid analysing the system for what it actually is and what it achieved and how those two things shaped and maintained one another.

In your example, why were the collectivisations forced? Why didn't the classes in the countryside voluntarily accept collectivisation? What was the shape and composition of the opposition to that policy and what were its results? What was the internal make-up of the party within those regions that led to their successes and failures? What could be done to avoid those failures in future? Were they inevitable? A dialectical approach would seek an immanent critique of the social system to analyse why history played out the way it did.