Coherence is kind of objective to begin with, so it's not so much "society puts coherence on the backburner" as it is "society puts YOUR idea of coherence on the backburner."
Lykathea Aflame is a bad example to use because they're an extreme case that seems, by design, not fluid, at least in the more traditional sense. The whole point is to come across as whacked out and juxtaposed. Sigh and Akercocke are probably other good examples of that, or Unexpect to an even greater degree. Really, death metal as a whole is kind of hard to pin down in terms of what flows and what parts work together because most of it through its history has been bent on eradicating more traditional song structures, melodies or transitions (more so than, say, power metal).
That said, I think there's often a relatively more universal consensus among many as to what music gels or flows well and what doesn't. As far as extreme music is concerned, melodic death metal is a good example. While it shares many of the basic traits of more straight-ahead DM, the approach is usually less free-form and certainly less atonal. I think it demands a more traditional and less meandering sense of songwriting to catch on, and the bands that accomplish this are the ones who stand out and get noticed first. That's why I think a band like Amon Amarth manages to stand out; even though it's an overdone style with relatively simple structures and little technical prowess, the writing and parts come off effectively and have an extremely fluid and unifying effect.
