There is definitely at least a little luck. Vontaze Burfict was Aaron Curry with a glacial forty time and with even less ability to stay in control. And they made him into a productive player somehow.
I think the answer is pretty simple- there has to have been some kind of change in the scouting department. Every year since 2009, the Bengals have been year in year out among the best drafting teams in the NFL. I'll admit some bias, since they draft more players I like than just about anyone else, but I think the results are really starting to show.
I don't know if Bernard fits a physical team like Cincy, but he's a good RB who can slip through small spots and rack up big plays. Last year they had a dead average running game with a below average starting RB. I like Bernard, but that said, if the Seahawks end up dangling Marshawn Lynch in trade talks next offseason, I'm guessing the Bengals would among those in on the discussions.
While I think Dalton's absolute maximum upside is a less clutch, less composed Troy Aikman, that might be enough if they can get a real running game going. Cincy's defense finished #3 in weighted DVOA. A good running game will take them places. Tyler Eifert is going to be a very good weapon on 3rd down / redzone situations, too. He might be the best jump ball target I've ever scouted.