Often used to describe bands like Pantera and Exhorder. With mid-tempo riffs similar to those found in Thrash Metal and a tendency to focus more on groovy syncopation and heaviness than outright speed.
Tormentor - Tormentor I - Anno Domini (1989)
Bathory - Reaper - Bathory (1984)
Winterfylleth - The Shepherd - The Harrowing of Heirdom (2018)
Dimmu Borgir - Tormentor of Christian Souls - Enthrone Darkness Triumphant (1997)
Thelonious Monk - Just A Gigolo - Monk's Dream (1963)
Ritual Chamber - The Eternal Eye - Obscurations (To Feast On The Seraphim) (2016)
Heads for the Dead - Of WRath and Vengeance - Serpent's Curse (2018)
Gorguts - Inoculated Life - Considered Dead (1991)
1349 - Slaves - Massive Cauldron of Chaos (2014)
Nattravnen - From The Haunted Sea - Kult of The Raven (2018)
Subjectively, I agree with you on both counts - it's always sounded transitional and thrash/heavy metal influenced to me, and I find it kind of boring. But you can hear where it was going. The real roots are what those guys and a handful of other bands were playing in the early to mid 80s, and at least we have some documentation even if it's just crappy demo recordings. Funny to think of that stuff as being so old and obscure and then compare it to all the high-polish studio music coming out at the time.