I know this is your opinion. I won't argue the takeaway numbers, because they've legitimately been bad. Beyond that, I believe most of the evidence would suggest that the defense has been improving gradually over the time Marinelli's been here and as we've added talent. There was a time when neglecting the defense in both the draft and FA actually killed us, yes. But that was a while ago now.
0-16 as a HC on a different team isn't really all that relevant to his performance with the DL, which is what this thread is about. There's very little serious doubt about Marinelli's qualifications as a DL position coach. If that's the argument you're making, you wanna check your head. He's a top DL coach.