"You can't have Death Metal band from a Thrash band, after all, Death Metal just appeared, out of nowhere. It really didn't come from thrash metal, with a extra dose of aggression, no, no, it came by itself. :)" - can't believe what I've just read, I don't mean to sound rude or anything, but someone should revise their "knowledge" of metal.
These guys at their prime i,e first two albums are the pinnacle of thrash. Nothing really comes close to their blend of technicality, savagery, and all out hellish speed. They make Razor look tame, they surpassed Slayer, and overall their discography is arguably better than Dark Angel's. Illusions may not be better than Darkness descends, but taking into account the fact Dark Angel tanked in quality afterward. I'm inclined to call Sadus superior