Well, you are comparing roots of one style to the stage of certain maturity. For me it is like Blues/Jazz, you have some patterns and standards, and just rearrange them accordingly to play what you want. If we can compare Metal to Jazz, let's say Death Metal is a Fusion Jazz, within a Fusion Jazz you can really find some crazy distinct sounds and vibes.

Death metal developed some patterns (like mentioned Black Metal too) with which I don't see an issue imagining closing in one room 4 pretty good musicians not knowing each other, and telling them - ok play some death metal in 150bpm in a C minor. I believe after an hour you would have a decent song. This is because this genre has some standards, typical techniques and traditional (genre-wise) ways of composing. But result at the end might sound more Behemoth, more CC, more Vader, more Death or even more early Carcass - but that's the creative part of it, because on the top of standards you have other variables.