Imperialism isn't hidden. It's readily observable what is done, and who benefits. Capitalists don't really have a reason to be categorically sneaky. It's done through proxy war, installing governments sympathetic to international capital, destabilizing regions, and so on because those are strictly more advantageous and more profitable than outright conquest given current conditions. I'm surprised you would deny that point, look at the Bush boondoggles in Afghanistan and Iraq. The most advanced military in the world can't effectively occupy two countries against insurgent cavepeople with beat up rifles and improvised explosives. Look at the string of colonial wars in the British Empire, which in many ways relied on an arms disparity that no longer exists to be effective, and were nonetheless costly.
You really have to view it as an evolutionary process akin to natural selection or game theory. If it is more profitable under current objective conditions for party A, a state representing the interests of several capitalists, to take a certain action than its alternatives, it gets a competitive advantage or looses a disadvantage against party B and can then accumulate, or stop loosing, power. If party B (and others) does the same, the paradigm changes to that new action, and if they do not, they diminish in relative power and importance to where those agents who adhere to the new paradigm, and thus the paradigm itself, come to dominate. There's no mysticism here, it's a matter of rational economic self-interest. People don't even need to be cognizant of those interests for the process to function, again, as with natural selection.
Capitalism isn't an "absolute idea," it's an emergent property of the rational economic interests of those who demonstrably hold the means of production.
I don't see where this is done. If you mean that using historical/dialectical materialism to explain society is begging the question, literally every worldview asserts premises which then imply its conclusions (provided the logic is sound.) Hell, even in physical sciences you need to assume the universe exists, is observable, is governed by laws invariant over space and time, and which can be approximated by models with predictive capability. But chemistry is hardly a circular philosophy.
It's technically inappropriate from the standpoint of Marxist theory to anthropomorphize capitalism and ascribe it goals and a volition "of its own," since it's an emergent property of individual material interests structured in a specific way we can analyze, and not an autonomous entity, but we often do so informally when it's clearly a metaphor, and always with fundamental causes in mind. Tying it to its fundamental causes around things in the real world (say, MoP) is the "materialist" part of the theory, no less! Even in orthodox microeconomics we talk about how an equilibrium ''responds to pressure" as a demand curve "shifts," in chemistry we talk about where electrons "want to go."
Your critique here applies to everything and leaves nothing. It reduces to solipsism.
This, however, is a valid point, and I'm myself rather skeptical of the work of the Frankfurt School.
Popper's falsifiability criterion is flawed in a similar way. There's no formulation of the social sciences which can satisfy it.
It's important to point out here that SJWism is rather easy to critique "according to its own rules" and effortlessly contradicts itself, almost wherever you look, just as Marxism exclusively critiques capitalism within capitalism's own internal logic and rules. Dialectics, the analysis of something's internal contradictions, is really the tool we have to weigh up "meta-narratives" against one another. If you have another one, shoot, but otherwise your position defaults to either postmodernism or some other radical subjectivism.
Besides, something like
essentially brackets metaphysics
