I think it has to be Samsara's list, with maybe a bit of Stadler in there. I wish I could add to it, but--and I'm not criticizing the OP at all--the criteria are so narrow that they necessarily restrict discussion to only a small number of players. In light of that, not really sure what can be added, both in terms of names and discussion.
But to add to the case for Hetfield: There isn't a single thing he was doing that might be described as "innovative." But what he did in totality still fits the description of "innovative" in my mind. He played heavy, he played fast, he used a lot of muting and percussive playing, he incorporated a lot of classical influenced and combined them with punk influences, and he played with very clean, precise technique. In combining those elements, he was doing something innovative, in my mind, especially as it developed into a signature style that helped launch an entire new subgenre of metal (and, yes, I know Metallica didn't "invent" thrash by any stretch--but they brought it to popularity and created a recognizable brand). That, to me, qualifies him, or at least puts him in the discussion. He wouldn't be on my personal Mt. Rushmore, mind you. But I think he arguably fits the criteria laid out in this thread.