Responding to this a little late.
While I'm not old enough to have seen him play, I'm somewhat of an hockey historian and have watched old tapes.
There's no doubt that Jean Béliveau would dominate any era of history. Even today he'd still be a tall and skilled #1 center and the greatest leader the sport has ever seen. He was also a complete player—think a Crosby type (not stylistically, but in terms of being complete).
Historically, Béliveau is at worst the 3rd greatest center of all-time, and center is the strongest position by far, so that says a lot. There's an argument that he is in fact the greatest center of all-time, over Gretzky and Lemieux, because of his all-around game and leadership—in that sense, Béliveau is a better franchise player than Gretzky and Lemieux. But that would be a controversial opinion, so let's leave it at 3rd greatest center of all-time.
Among all positions, I cannot see Jean being ranked further down the list than 6th greatest player of all-time, and he is often considered the 5th greatest after Gretzky, Lemieux, Orr and Howe. Béliveau's competition would be Bobby Hull, Doug Harvey, Maurice Richard, Patrick Roy, Howie Morenz and soon Sidney Crosby. That's my opinion but it's roughly shared by many other amateur historians, whatever that's worth.
The thing with Le Gros Bill is that his resume is flawless in a way that nobody else is (except maybe Doug Harvey and Gordie Howe). Gretzky was unidimensionnal, and it can be argued his Oilers underperformed given how strong they were. He also failed to win when he started declining, though he came close. Lemieux had so many injuries, and he too was unidimensionnal. Bobby Hull only won the cup once and was difficult to play with. Maurice Richard again a tad unidimensionnal, plus some of his big seasons (the 50 in 50) came during the WWII depleted years. Howie Morenz had a good but not great playoff record. Patrick Roy had a good but not super-great regular season career—clearly beat by Hasek there. And Hasek has a weak playoff record against that competition. Crosby had a lot of injuries, and his game wasn't as complete in his youth as it is now. Plus the early-career antics.
Béliveau is a complete player, the greatest leader in hockey history, was #1 center for TWO dynasties, was strong and tall, skilled both as a playmaker and goalscorer, great stickhandler, high-IQ, stayed with the same teams for two decades winning 10 Stanley Cups, was an immense playoff performer and he did all that in his hometown as a french-canadian hero who had to replace a living legend in Maurice Richard.