Do you disagree with hardcore punk influence as being one of the key disambiguation between thrash from speed metal? Personally at least that's what I feel. I do understand this means for example a lot of Metallica won't count as thrash but I like to say if you slow down Metallica it sounds more like Black Sabbath while slowed down Slayer or Anthrax sounds quite different, so I feel there may be a hard physical evidence for my theory. I found it a bit odd you didn't have this aspect written in the statements about differences between speed metal and thrash metal.
I do like and agree that you put Slayer - Necrophiliac under the development of death metal. Though by those same accounts I'd have moved Kreator - Ripping Corpse from the thrash column to the death metal column, but that's just a personal line.
I also feel your tech death is biased too much toward 2000s rather than stuff like Sadus, Demilich or Disciples of Power.
Absolutely loved the inclusion of death n roll, one of my favorite substyles.
Well, sped-up Cathedral sounds like Bathory so... I don't know what that's physical evidence of? But I accept your theory as a valid theory, just because there's a test for it, even though I don't understand what the test shows.
I think Cathedral is closer to death metal structure in my personal view compared to classic Black Sabbath, so that should not be too surprising. My test is simple, the history of thrash itself shows a lot of it coming from combining hardcore punk influence directly to metal, a lot of old thrash feels to me having mild to overt hardcore sections or riffs at points. And I think that's the aspect that gives thrash its political themes and more direct lyrics compared to the more fantasy or generic bragging style of older metal.