Jennings is one of the best big play receivers in the game. Since 07, when Green Bay needed a spark, Jennings provided it. That's not overrated. Comparing him to Fitzgerald, Moss, or Andre Johnson is, but after those three, Jennings falls in line with the likes of a Roddy White.
The Bengals had good defense.
The Packers called plays down the field and Rodgers didn't have the time to see them develop so he couldn't get the ball off.
Jennings dropped a big throw too.
Those are the reasons why he was held without a catch. Using him as a decoy would be a terrible idea.