You bring up some interesting points:
In Degradation is the song that was used to gauge how one can better understand how a seemingly harsh wall of sound, is actually high art in the truest sense.
Bingo. In music, there are processes, and there are objects.
Let's start with objects. There are intervals between pitches, like the perfect fifth and the major third, that are aurally pleasing because they embody simple mathematical ratios, and are derived directly from naturally occurring acoustical overtones that we experience every day. "Dissonant" intervals, like the tritone, are less frequently encountered, and their derivation is more complex, making them thus inherently less "pleasing" or if you prefer, less "stable".
However, dissonant sounds can still be arranged in a way that is intellectually stimulating, in a process that is stimulating. This is why one can derive as much enjoyment from Beethoven as from Averse Sefira, even though one uses a greater percentage of dissonant sounds in its syntax. The lesson here is that
the syntax of music is at least as important as the vocabulary of objects it is created from. The evidence for this purely experiential, but if you need convincing, look at how vastly different composers like Bartok are from composers like Mozart in terms of the vocabulary of musical objects they choose to use, and yet both are included in the western canon, and are performed and enjoyed by similar demographics.
Consider also how many metalheads will profess, most likely genuinely, enjoyment of Beethoven, and in the same breath praise a band like Suffocation. One uses far more dissonant musical objects, and thus their surface aesthetic is quite different, and yet both are appreciated by the same minds. This is because the syntaxes of both the music of Beethoven and of Suffocation, their processes, are actually quite similar.
Once this distinction between object and process is understood, it's in fact easy to apprehend how "a seemingly harsh wall of sound, is actually high art". The harsh wall of sound you allude to results from the music being made from dissonant objects, and its function as high-art results from the processes that are defined by the arrangement of those objects. The song is in fact both these things; dissonant and beautiful.
This relates to an interpretation of the idea of "pattern-language" that used to exist as a hero-worship page for Christopher Alexander on the old ANUS site. It described how one idea of how the world actually functions is that instead of saying that "beauty" only exists when certain static criteria are met, we say instead that there is a language of beauty, accordingly within which many things, indeed anything can be expressed.
We might then say that metal music uses the language of beauty to describe darkness, which can be directly related to the distinction we were just discussing between object and process; the processes of metal are beautiful, while its objects are ugly. The true innovation in metal from this standpoint then is the ability to address darkness in creatively beautiful ways.
Of course metal was not the first to do this; it's helpful to remember that we have predecessors. John Milton, Ludwig Van Beethoven, Hieronymus Bosch etc. all at one point in their lives could be said to have engaged with the above distinction in their own way. What still puzzles me is why this oppositional or adversarial nature of aesthetics, one that implicitly engages with opposites like light and dark, truth and lies, beauty and ugliness etc., is so enduring when most developed philosophies in Western nations point to this distinction being a convenient fiction, usually most convenient for the Christian church, for whom it served the purpose of conquering and focusing an entire continent of pagans. Why do our artists persist in using it, and yet our philosophers and scientists do not? Metaphor of course has great control over the passions, but if the distinction between good and evil is untrue, or at the least unrealistic, then are we justified to use it at all, let alone in art? How can we read "Beyond Good and Evil" and then listen to any occult or religiously themed music and keep a straight face?
Thanks to anyone who gets or reads this.
Initially, suspira intro aside, an emotion is introduced (0:29 -1:08), then the experience which invoked said emotion (1:08 - 2:31). After the introductions, the emotion is explored (2:31 - 3:33), then a realization occurs (3:33 - 3:58) followed by a reference to the experience (3:58 - 4:25). This piece could end here really, making it lower grade metal, but it doesn't, which is why it's high art. The emotion fights the realization (4:25 - 5:35), then succumbs to a full realization (5:35 - 6:00) and subsequently falls into congruence with this full realization (6:00 - end).
This is great! A few things:
-You're using vernacular vocabulary to describe music; it's better to use terminology specific to music for analysis in the initial stages, to help with specificity. Does the music get louder or softer? Faster or slower? Of course you can take this as far as you need to in complexity to describe what you think is important about the music and how it communicates its experience, but these are just starting points. Don't use a terminology list though; the best way to internalize musical terms is to become a musician of some kind.
I should also mention however that, provided you've mastered musical theoretical terminology (and that is an ESSENTIAL prerequisite for the license I'm about to describe), you will probably reach a point in any analysis where conventional musical terms no longer serve you; in these cases you may be forced to invent or commandeer new terminology, and you should not be afraid to do it. If it's a crescendo, call it one, but if truly no word exists for what you hear, then use one that seems most appropriate to you.
-When I listen, I can identify clearly every section you've described, but as far as I can tell you mainly address riff structure and texture. What about the grammatically deranged and visually surreal lyrics? How do they interact with and overlap the divisions you've described? They clearly change from beginning to end, and articulate different things along the way also. Do they create their own unique sub-structure?
What about the details of vocal delivery? Do they enforce the patterns you've uncovered, or create new ones, or both?
And finally, that intro! It's not random, and you shouldn't throw it away so hastily in your analysis. Doesn't he mention a doorway as the riff fades in? Does he not also mention that the living death is behind that doorway? Seems pretty significant to the meaning of the song.
All this being said, I'm impressed by and in general agreement with how you've parsed the riffs in this song, although I would have used different labels for the sections.
For example, for the slow diatonic music with keyboards you generally favor the term "emotion", while for the more chromatic pitch content without keyboards you use the terms "realization" or "experience". You even pick up on some fairly subtle riff relationships, like between the sections from 3:33-3:58 and 3:58-4:25, by designating one as a reference to the other. What could be interesting to explore, if you're interested in these things, is what gave you the impression of this relation. There must be a reason your ear, and mine also, hears a relationship between these two riffs. I think here it has to do with the keyboard melody: the contour of the melody, if not the exact pitches, is very similar between the two sections.
All in all, I enjoyed your analysis, and like the best ones, it helped me to understand the music myself, and provided fertile ground for further exploration.