DSO is just as clearly derived from the previous generation of 'avant-garde' or 'post' black metal (Ved Buens Ende, Dodheimsgard, Fleurety etc.), with more than a little nod to past hipster rock heroes like Sonic Youth (an influence common to much of the current generation of metal marketed for an indie audience).
Prozak says it well in the ANUS review of T.A. "In the use of pulsating split arpeggiated power chord progressions played off against half-speed resolutions, one can observe the better influences of later blackmetal, namely Antaeus and Deathspell Omega (and Graveland)." I think this is demonstrated well if we compare the Averse Sefira track "Hierophant Disgorging" with, say, "Sola Fide II" from Deathspell Omega.
I think you are right to notice the death metal influence in Averse Sefira but I disagree about the "indie marketing" of Deathspell Omega (At least, certainly on everything up to Fas.). Fas has some transitions that I dislike when I listen to them out of context, but the driving force of the album is a pronounced Obscura-era Gorguts influence. (On an album-by-album level there is a clear comparison between the development of Gorguts and Deathspell Omega).
I don't agree that DSO's composition is "plug and play". Kenose and Si Monumentum, in particular, are unified conceptual works with a nearly symphonic gambit of moods. In particular I think that the "prayers" on Si Monumentum are an excellent structural device.
I don't know the bands you mentioned (Ved Buens Ende, Dodheimsgard, Fleurety etc). Am I missing anything?
The influence of DSO has been, overwhelmingly, to raise the intellectual standards of black metal by moving the genre towards a theology. I feel that Averse Sefira grasp for this religious sincerity on T.A. but do not quite realise it. Part of the reason for this (moving to Neoclassical's post) is the clumsy nature of their lyrics. Perhaps I would have done better to express them as being "too contrived" as opposed to "too obvious."
Numbing states of languish
Surging across aspectual abyss
As an obstacle of motion
The equanimity of struggle
Gilded in guilt
All fetters melt away
Releasing the pulchritude
Obfuscated in the face
Of the moral
I may be wrong but, based on the intensely disjointed style and lack of lyricism, my intuition is that someone plucked uncommon words out of a thesaurus in an attempt to appear sophisticated.
In any case, compare the above with:
Everything, except GOD, has in itself some measure of privation. Thus all individuals may be graded according to the degree to which they are infected with mere potentiality.
I find this to be, if not religious, at least authentically theological and certainly genuinely evocative and sinister.