What you wrote makes sense, If putting a player on injured reserver didn't free up a roster spot. Since putting him on IR does free up a roster spot, then he's not just taking a spot from someone else.
Or, you are saying Fujita can only naturally back up Gocong, and has no other use so cutting him presumes Gocong will not need a backup, or that others are better than Fujita to backup Gocong.
I'm saying Fujita is one of the top 5 linebackers on the team, they'll find a place for him.