I think to see a specialist defender in the team they would need to be able to make a lot of their tackles one on one (maybe another player or two join in just to slow things down but old mate does 90% of the work).
If you aren't offering much in attack you need to be making a really significant amount of extra energy available to your teammates by taking on defensive workload. If they could make like 30 one on one (or virtually one on one) tackles and then help out with another 15 or so tackles of other players is that worth an average running stat of 4 runs for 34 meters?
Maybe do a bit of first receiver just to help move the ball along wider to a prop or a half and contribute in attack but then I guess if they be trusted to do that why isn't this defensive weapon able to run the ball?
If they can't trust their handling to even do that is it really worth playing 12 on 13 when you are in attack?
Not sure how easy it will be to play away from them either, certainly there would be time you would do it. ie hooker looks up and sees Nigel Plum jnr on his right so he just passes left instead. Obviously you can do that with players now (more often to run at someone than run away from someone) but when it is the guys only job it becomes a lot more impactful when he isn't doing it.
I don't think Rugby League (without much more significant rules changes) you would see an extremen degree of specialisation.
