I think you're wrong tbh. How does something like the groovy riff in Butchers of the Sea not remind you of death metal as a musical style? I don't care about it having a "relation to death metal" on any other level other than sound-wise, tbh. It sounds like death metal some of the time. I don't think influence is the correct word if I get what you mean (that Mark is not going "hey I like death metal time to throw some in"), but I think there are parts that sound very much like OSDM (heavy, grooving chug riffs with minor key melodies and dissonance as you mentioned). Also recommend me more old heavy metal with death metal sounding sections, as that should be cool to hear (not being sarcastic, I really do want to hear more since it's kewl here).
Also, I kinda disagree on country influences, as I feel that sorta cheapens Tree of Life, but it's definitely a little different...like a heavy acoustic folk song or something.