I think people need to stop making generalizations and blanket statements like "player x was better defensively than player y," and instead should actually explain what they mean.
When it comes to defending the opposition attack, I think Orr, Lidstrom, Bourque, etc. are amongst the greatest of all time. I personally would take Orr over just about anybody in this regard, but I am not at all offended if someone would rather have Lidstrom or Potvin or Bourque. Valid arguments can be made for all these guys. They all blocked shots. They all had impeccable stickwork and stick positioning. Some were more physical than others, but they all could get the job done in front of their net.
That being said, Orr was far and away the greatest contributor to his team's defense in NHL history. Why? Because he controlled the puck ALL THE TIME. The best defense is keeping the puck away from the other team, and nobody did that like Orr. So in that regard, Orr was easily a "greater defensive player" than Lidstrom and company.
Also, this is the same reason why I have problems with calling Gretzky a poor defensive player. Yes, he was not the best at defending the other team when they had the puck, and he wasn't the best backchecker. But more often than not, it was a moot point because Gretzky had the puck on his stick and he didn't need to backcheck.
EDIT: To address the actual OP's question, my belief is pretty similar to the general sentiment of this thread. Orr probably wouldn't be able to skate laps around people and play keep-away anymore, just because the speed of the average player in the NHL is so high. The game is different, things like that cannot really happen anymore. Orr would still absolutely dominate though, just like any great would if you placed them in another era. If I were to put a number on it? I would say Orr would still pot home between 30 and 40 goals every year, and 70-80 assists every year.