Ryan did it for one season then Payton forced him to go to a standard 4-3-4 because Payton was obsessed with trying to be the Seahawks defense.
Allen took Ryan's 4-2-5 and basically perfected it. Ryan's 4-2-5 was from necessity due to lack of talent at LB, Allen said "We're going to specifically build into the 4-2-5 look".