Regardless. He proved nothing coaching the Bills line. Anyone not named Wannsatche could have got production from that line. As for the being "next in line" for a DC position, he had his chance in NE and despite being a line coach for 9 years (not 14), he was suddenly let go by them. Not only was he not considered for a DC position by NE, but he wasn't even considered for one by the rest of the league. And, now, he still doesn't get a DC position. So, maybe he is proven, proven not to be DC material.
As it was under Pettine.