@Peer Bard Deleuze, imo, wouldn’t agree with the qualification «materialism», he would have preferred something like «immanence», and instead of «dialectical» he would surely have said «problematic»...

I've been wondering the same. The idea of quantitative-to-qualitative change seems to me very similar to the ideas of extensity and intensity. There is an overarching conflict I think between the Hegelian "dialectic" and what I think what Deleuze calls the "rhyzome". DeLanda puts it differently, he says assamblages are not made by (the hegelian notion of) relations of interiority, but instead, relations of exteriority, which mean that they are made by heterogeneous elements which are not dependent on a fixed identity of wholeness, but as "rhyzomatic" association. I think that could give a clue to that, but I'm not entirely sure that's all to it.