You tell me better defencemen defensively than Orr
Here's the thing, it's impossible to do so and here's why:
1.) Someone would have had to be old enough to watch Shore, Harvey, Orr, Robinson, Savard, Stevens, Lidstrom and the rest. And, even then, it's only one person's view.
2.) There has to be a clear definition of "defensive defenseman". Do you mean this is a defenseman who prevents goals? If so, TOI and +/- would be a main factor. But people have different views of what makes a defenseman great defensively. Some prefer a physical type like Shore, Robinson, Stevens, Langway, Chelios and Pronger who make their opponents pay a toll when trying to score. Others prefer the technicians like Harvey, Savard, Niedermayer and Lidstrom who are extraordinarily sound and play mistake-free hockey. Some prefer the complete package types like Orr, Park, Potvin, Bourque and Fetisov. So, it comes down to personal preference. All of these guys mentioned are among the greatest defenders of all-time, and any of them would be a coach's choice to hop over the boards on the PK or to protect a 1 goal lead late in the 3rd.
The bottom line is there is a trophy that recognizes the best defenseman to play the position each year. And the fact is, Bobby Orr won more of them than anyone and played a lot less than any of those other greats I mentioned.
And I know this is hypothetical, but does anyone believe in their heart that IF Orr played 16 full seasons instead of 9, that he wouldn't have ended with at least 11-12 Norris trophies instead of 8? I mean, that would only have been 4 more in 7 additional seasons. When Orr was no longer healthy, here is a breakdown of the next 7 Norris winners:
Potvin x3
Robinson x2
Carlyle
Wilson
So, if Orr was healthy for those years, I would offer a guess that Potvin and Robinson may have snagged one or so each, MAYBE Potvin 2x. But there is no way on earth that a healthy Orr at age 31 and 32 would be losing Norris trophies to Randy Carlye and Doug Wilson. Hell, now that I really think about it, Orr PROBABLY would have won all 7 of them and ended up with 15 Norris trophies when it was all said and done. Because this man literally had a grip on the Norris the way Gretzky did with the Art Ross.