Why the Hegelian dialectic, and not the Materialist dialectic? Marx's advancements on Hegel are, to my knowledge, near universal in accrptance among dialecticians, as Hegel could never escape the trap of his Absolute Idealism. Hegel's insistance that everyone moves towards their own self-interest, and that this advances the universal Spirit, are wrong, but Marx's correction on the dialectic to return it to the economic base and Materialist outlook are what brought about Historical Materialism.

If you are speaking on the Marxist dialectic, then your critique doesn't follow outright, as Capitalism has changed into Imperialism, and Imperialism is what caused the Russian, Chinese, Cuban, Vietnamese, Korean, etc revolutions. Each of these new Socialist systems is still stamped with what came before it, as is consistent with Materialist dialectics, so this may already be what you're getting at, if I'm reading you correctly. Resolving contradictions is a historical process, not a mental one.