Most metal singers don't employ fry screaming or false-vocal chord growls. Those are limited to certain sub-genres, which, at least in the "big picture" of metal, aren't terribly common. They've become more common over time, though.
I have no idea what "most honest" could possibly mean here, and there's zero thrash on any Tool album. Tool spawned from the alternative rock/metal movement of the early 90s along with bands like Faith No More and Jane's Addiction. All very different bands with very different takes on metal. Tool has undeniably has the most staying power and have a rabidly obsessive fanbase who feel their music holds the key to the meaning of life and the universe. I don't go that far, but I get it.
In any genre the vast majority of artists within that genre are going to be generic, predictable, formulaic, etc. because that's just the nature of human creativity. Those we consider "interesting" will depend upon our tastes and temperaments. I like Voivod too. They were among the pioneers of what could be called "progressive/technical thrash," and certainly the most well-known band of that sub-sub genre. Nothingface, Dimension Hatross, and Killing Technology are all great albums for people who love more technically advanced 80s thrash. Perhaps the best modern band to have adopted that sound (and combined it with a bit of black and death metal styles) is Vektor, and their 2016 Terminal Redux is one of the most acclaimed metal albums of the 2010s. Sadly, they've since broken up.
It's not really my view since that's just what the sub-genre is called. Typically the "tech" label refers to the technical difficulty of playing the music. I haven't learned to play any Voivod songs so I don't know how difficult they actually are; I just know they're thought of as one of the sub-genre's key early bands.
