Okay, sepultura69, look at this way. Forgot all this stuff about founding members/main songwriters, blablabla... Max was the VOICE of the band (pun intended).
What made Sepultura different than all the other thrash bands? Max. Simple as that. Yeah, I know he's just a frontman and all, but when people heard old Sepultura I doubt they said, "Wow, these riffs are like nothing I've ever heard before. These guys have the most original thrash sound I've ever heard." They probably said something along the lines of, "Wow, this guy has the coolest thrash yell I've ever heard. I don't think I've ever heard anything like it."
So what I'm trying to say here is that Sepultura today could sound like old Sepultura even with one original member/main songwriter, but it's not worth it without Max.