I think even if Smith had stayed in St Louis the Rams defense was not going to have the same productivity they did last year. Bulger threw a lot of picks but the Rams defense was exceedingly opportunistic, so it didn't hurt the Rams as much as it should have. The Rams had the most takeaways, five more than second place Baltimore, but also lead in giveaways.
The problem the Rams are going to face is that they had 22 fumble recoveries last year, no one else had more than 17. It is highly unlikely that they will again get that many fumble recoveries. Now I know five more fumble recoveries doesn't sound like much but that's almost a 1/3 increase over the second place team, so it is significant, and went a long way towards masking Bulgers mistakes.
While it could be argued that forced fumbles are a result of a defensive teams skill, the actual recovery of the magic bean is another story, and I would say luck factors in more than anything else in the game, except for Ruben Brown getting elected to Pro-Bowls every year.
So, I think unless the Rams fix Bulgers interception problems, their offense and defense are going to look worse than the 2003 version of the team. Regardless of who is defensive coordinator.
Hopefully, the upgrade in our offense, coupled with our familiarity with his defensive system will allow us to shell them this year.