Yeah I knew the Rams were in trouble on defense that year during preseason, they looked bad and it translated into the season.
This was Mike Martz first mistake as the defense worked fine with Peter Giunta calling the defense because he knew that defense from Bud Carson as they had worked together, but pairing Giunta with John Bunting, who took care of ensuring everyone was in the right place and being able to orchestrate the defense to the players plus motivating them accordingly.
Giunta & Bunting were Co-Defensive Coordinators for that reason and after Vermeil resigned, Martz decided he wanted Mike Haluchak as his linebacker coach and then informed Bunting that he was going with Giunta as the DC as he didn't want co DC's and that he was hiring Haluchak as linebacker coach so Bunting understood he was out. IMHO Martz should have kept Bunting as the DC, however, Bunting vacillated signing his contract to comeback with the Rams because Martz went with Giunta, Martz then replaced him and the defense suffered.