The Bengals went 9-7 and made the playoffs last year. They also went 10-6 and won the division two years prior to that in 2009.
Two years prior to that The Browns went 10-6 and lost a tie-breaker for the division crown. The Bengals were 7-9 that year.
And in 2006 The Bengals were a .500 team, following an 11-5 division winning 2005.
They have definitely not been powerhouses. But I think you exaggerate a bit.