I deleted my original comment because it wasn't worded very well and came from a place of frustration and exhaustion. But what I was attempting to get at with "context-dependent dynamics" is that the model of history described by Marx can't be claimed to hold explanatory power in every possible aspect of sociology/anthropology/social sciences generally, because that's not how any model of anything works (as you said). Whenever I get into these conversations with MLs, it feels like they can't conceive of there being an aspect of how the human world works that isn't reducible to class struggle and dialectical materialism. Comparing it to physics, it's like they're hearing about quantum mechanics and all the extra complications and nuances that introduced in order to explain results that classical physics couldn't, and just perpetually going "nah, classical physics has been right about everything else. We must just be mismeasuring these results."