In his letters (I can't remember where exactly) Marx actually does mention at a point that he also considered Capital to be a work of art. It is definitely very literary, especially in certain sections with their descriptions of the experiences of the working class, but that literary quality definitely doesn't preclude it being scientific or relatively clear, if difficult, and even he could have been clearer (including by making it less literary, although then perhaps it might not have been quite as successful or moving).

Adorno imo is an actual example of intellectual masturbation. I tried reading Against Epistemology and I found it pretty impenetrable, even when you've read Hegel. Hegel is obviously not easy and I think could be clearer (Force and Understanding in the Phenomenology is something I've reread I dont know how many times and I'm still not sure what the argument is in fine-grained detail).