It may be a matter of opinion. Most old school dm, like Pestilence, Athiest, and Possessed, was very thrashy. Morbid Visions was definitley a death metal album, that is for certain, and most people would agree. However, I also consider Schizophrenia, Beneath The Remains, and Arise to be thrashy death metal. Chaos AD is definitley not death metal, and more thrash with a hardcore edge. Roots and their other albums from then on are somthing like heavy mallcore.