I get excited for bands like Portal and Deathspell Omega who fall into this sort of category (post-metal is probably an accurate term but it sounds stupid as hell) because I get excited for the actual musical development and these guys are uncovering some interesting territories.
I am myself addressing the Deathspell Omega question. But as I listen to Paracletus I have a feeling of confusion. When it is not basically and honestly speaking alt rock that is being played (which is often), there are fragments of music which, on their own, are quite amazing. However i am fearing that all these fragments fit together like all the -core stuff we criticise; that is, badly. I feel no overall sense of direction in the narrative.
And i am fearing that their 'ideology' is pure wankery. "metaphysical satanism" indeed.
The idea of "metaphysical" Satanism is fairly well thought-out but poorly named. As with any reference to Satanism, most people will automatically jump to the thought of Satan as the antagonist to Christianity, where in fact the DSO guys are trying to present a picture of powers and forces that move beyond the Devil/God duality (much like Crowley's work, often misunderstood when seen through the warped lens of dualism that the West is so wrapped up in) . This is really the fault of those who choose to reference Satan in their ideas but it is unfortunate because a lot of the ideas are fairly unique and streamlined. A poor choice of word, "satan". In short, it is basically worship of chaos, which is legitimate today as science has revealed to us underlying universal motivators like entropy and Heisenberg's principle of uncertainty (which, without, our universe wouldn't exist).
Truthfully though the theological context in which they present their ideas is hit-or-miss depending whether references to Satan get a person excited, and those that are excited by a "Satanic" presentation are usually not prepared to set aside their conditioned dualism and contemplate truths that simply "are".
As for the composition on a pure level; I really don't think they fit their (admittedly disparate) influences together badly. Confusing, surely, but that is what happens when completely new ideas are introduced. They have to spring from an already solidified framework. If alt-rock and late black metal are the aperture from which they construct their new content, so be it. It is not a smooth fusion, to be sure, but it is *something* new and that is what matters most.
First, you say that art is essentially a translation of abstract ideas. It begins as a pure idea that is translated and presented in a relatable context. That, I think, is an insightful starting point.
In the translation process, however, there must be "impurities" introduced into the originally pure ideas. This is due to the fact that no two individuals can possibly achieve the same pure understanding on the most basic level (and this is true because, for such a thing to happen, the atomic configuration of your brain would have to be precisely identical to mine, and we know that such a thing does not occur). Therefore, the "art" that we get is really a diluted, impure, and/or mutated form of the original pure idea.
This means, then, that the art, upon creation, becomes an entity of sorts that exists independently of its creator. Whether or not it serves the creator's purpose or function is still relevant at this point, but depending on the depth of abstraction, it is possible that the art will be "misinterpreted" or reveal new ideas to other individuals. Then, those individuals who experience the art not as a direct interpretation of another's ideas, may treat the art as it's own entity that deserves to be nourished and mutated further.
So it seems to me that this is what is happening with death metal currently. The core ideas have already been presented with as much lucidity and clarity as possible by the originators; now, it has been long enough that the ideas (relevant or not) have been diluted as the music itself has passed from mind to mind and been diluted/mutated further.
So, Portal really has nothing worth "saying" in terms of presenting new criticisms of humanity's behavior or suggesting alternate paths for humanity, and they shouldn't need to; "preaching to the choir". Nevertheless, the actual physical mechanisms that the musicians employ are allowed to continue evolving, degenerating, or mutating, because those styles and techniques now exist independently of the original ideologies espoused by originary death metal bands. And, that very manner of treating the musical techniques as worthy of developing on their own, independent of ideology, is how death metal got started in the first place. Therefore, we can expect something new to emerge eventually.
tl;dr - I'm a composer who is excited by unconventional music. Portal makes me horny.