Dialectics is within ontology/metaphysics, it is a way of describing the world/a norm on analyzing it. I am not personally convinced that everything is dialectical but that's as much criticism of Derrida and its trace as any Hegelian type stuff, but as a simplification it is useful for understanding feedback loops so very advanced for someone in the 19th century just not the end all be all. Metaphysics itself isn't useless, it is what frames the debate consciously or unconsciously, knowing yours and your enemies can make a world of difference on understanding how you should approach the situation (e g, someone believing in race essentialism should have their head bashed in), and the key here is to understand that metaphysics/ontology is inherently normative so it has both an impact on ethics (and vice versa) and can be useful practically (eg workers are essentially a relation of production). Any shit that talks self seriously about a descriptive metaphysics is too assured about his individual capacity to pierce a supposedly existing veil of truth that also, coincidentally, has supposedly not been pierced by anyone else, but centering workers, centering dual change, centering production relations, centering large blocks of society, are all useful ways to create the basis for a positive change of society (towards communism)