There are a lot of reasons why signing Floyd is good for the Rams. He can set the edge which has been a problem for the Rams defense for too long. He is a good tackler as well which the Rams have been very weak at. He has had a high percentage of dropbacks in coverage for an OLBer and is very good at it. His versatility can't be underrated in the Fangio/Staley defense which he already knows.
Staley will be using the Fangio defensive system, with some tweaks, that requires OLBs to be able to drop back in coverages. This allows him to disguise different pass-rush packages. Offenses have a hard time picking up the pass rush when they aren't sure who is rushing. The Bears used this system to stymie the Rams offense as we all painfully remember.
If you're just looking at sacks then remember Fowler had 2.5 fewer sacks in his first four years than Floyd had. Floyd could get the sack stat up near double digits. The Rams lost three starting LBers in Fowler, Littleton and Matthews with only Ebu having extensive experience remaining on the defense. In Floyd, the Rams have added an experienced versatile every down LBer that they simply didn't have and need.