The aesthetic of instrumentation is vastly different. Subtract the vocals from a Dragonforce song and then from a Wormed song. I guarantee that if you perform your little experiment and tell the listeners that "one of these tracks is power metal, and one is death metal," they would be able to tell the difference.
You're trying way too hard to conflate musical styles based purely on names of techniques. A power metal blast-beat is implemented differently, and accompanied by different musical complements, than a death metal blast-beat. Furthermore, the melodic structures of power metal borrow from entirely different chords, scales, and modes than death metal. Vocal style has the least to do with it.
You are again missing the point of what I am saying. In your version of this experiment, you're asking participants to identify death metal by what isn't there (I have been talking about the vocal style, so removing it from the equation does not work here). All of those nuances and differentiations you speak of are true and exist, but what I am saying, again, is simply that they are
less identifiable than full on gutteral death metal vocals. Get your mother in the room and ask her the primary difference between Slayer and Wormed or Skinless. She will surely tell you the vocal style. Yet again, so we're clear, because I know you are going to reply and say, "yea but death metal vocals alone don't make the genre"...this is correct. Surely not alone, but as the main differentiation between it and other genres of metal.
edit: for the sake of arguing from authority, I have gone back and tried to find the quotes which I cited when I made this argument last year or so. The domains, unfortunately, have expired (the interviews are old). I think I remember exactly though, so you'll just have to take my word for it, but...
Chris Barnes
Glen Benton
George Fisher
.....all three of them have previously stated that the one, main thing that sets death metal apart from other genres of metal is the vocal style. Of course this doesn't make what I say true, and maybe you know more than them, or even disagree (as you have every right to) but I clearly side with them since they've been directly involved in the genre at a professional level for many more years than you or probably anyone else posting here.