The features you claim typical of death metal over the years were not something that existed in significant excess for Deicide to remove.
It's not a question of "excess" in others so much as Deicide distilling the genre to it's pure essence.
They weren't CC-level generic, yeah, and Legion was certainly more deathly than Death, Obituary, and others, but I don't see why those first two albums are considered to be unprecedented.
Perhaps because you don't have the listening experience to fully appreciate their impact? Seriously, listen to those albums in the context of the death metal from that era. Compare Altars of Madness or Leprosy or pretty much any death metal album circa 1987-1990. None of them even come close to matching the abrasiveness, the sustained dissonance or the sheer violence of Deicide, much less Legion, which upped the ante in every way.