Looking at that list:
Janoris Jenkins
Roger Saffold
Ndamukong Suh
Marcus Peters
Dante Fowler
Jenkins left after the 2015 season and E.J Gaines took over as a starting CB in 2016. In 2015 the Rams defense was 23rd in the league in passing yards per game at 254.1. In 2016 they were 10th in the league at 233.3 yards per game.
Roger Saffold: yup, the Rams' OL was worse off after Saffold left.
Suh left after the 2018 season; Sebastian Joseph-Day and Greg Gaines took over in 2019. In 2018 the Rams defense gave up an average of 122.3 yards a game (23rd in the league) and 5.1 yards per carry (32nd in the league - dead last). In 2019 the Rams defense gave up an average of 113.1 yards per game (19th in the league) and 4.1 yards per carry (8th in the league!!!)
Is there any question that the Rams' defense improved after the Rams swapped Peters out and acquired Ramsey? I know Peters did well with the Ravens aftert the trade but there's no doubt that the Rams defense was better with Ramsey than it was with Peters. (That goes to scheme fit and Wade's inability to adjust to Peters' skill set ... but that's another thread.
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The Rams had the 20th ranked defense last year. Let's see how they do this year before deciding if letting Fowler walk was a bad idea. (Also, the Rams will be able to sign at least one player next year who they couldn't sign in Fowler was on the books. Is that JJ? Kupp?)
AlbaNY_Ram