Making a point about Kansas City's terrible pass rushing defense (they only have six sacks), Adam Schefter writes that the Baltimore Colts were historically the worst of all time, "the 1982 Baltimore Colts set with 11 in the strike-shortened, nine-game season. In a full 16-game season, the 1981 Colts had 13 sacks." The Cincinnati Bengals, through 11 games, have only 11 sacks, on pace for only 16.
Interestingly enough, the Bengals have lost two defensive ends that's accumulated 32% of the team's sack totals after playing on terrible Heinz Field; could be a third with unknowns about Antwan Odom's shoulder, which would "improve" that to 50% of the team's sack producers suffering injuries; not that it matters, based on the fact the sack totals are so low, diluting the percentages. It is what it is.
The Bengals best sack-producing season was 2001, registering 48 sacks with guys like Reinard Wilson (9.0), Justin Smith (8.5), Brian Simmons (6.5), Takeo Spikes (6.0), Tony Williams (5.0), Darryl Williams (3.5), Oliver Gibson (3.0), Mark Roman (2.0), Vaughn Booker (1.5), Glen Steele (1.0) and Adrian Ross (1.0); I'm missing one. That team set a franchise record with sacks (48) and allowed 302 yards per game (best since 2003).
Since then, the Bengals haven't come close to replicating any success like 2001, which I believe if you take that defense, with the 2005 offense, it's the best Cincinnati team ever, issue of time traveling notwithstanding.
Since 2007, the Bengals didn't register a sack in nine games; shutout in 13 games since 2006; includes includes being shutout against Ben Roethlisberger, though he's been sacked 32 times throughout the season in his other nine games.
Lacking pass rush early in the season wasn't detrimental to the team's pass coverage and overall pass defense, which ranked in the top ten for most of the season. However lacking a pass rush has started to tire out the defensive coverages, allowing over 240 yards passing in four of the past five games, including 275 against Pittsburgh and 323 against the Eagles.
Other than a few highlight reels, the Bengals coverage has done as well as one could expect. Lacking a pass rush, with injuries mounting and a tiring defense, clearly nothing will change. So don't expect next season to produce immediate improvement. It is what it is.