It doesn't really give us anything meaningful. Drawing more heavily from the talent pools in the Czech Republic and Sweden is just as significant as drawing more heavily from those in Alberta and British Columbia. Nation of birth seems completely arbitrary when trying to normalize for era.
My original Canadian Norris comp is to shed light on how modern day guys compete against a larger pool than the 06 guys ever did.
Of course Orr or other great being better than the weak field in some years past are overlooked, not saying that Nieds is Orr but it's another bring out argument for certain players type of thing.
I don't think there is any formula for normalizing between say 56 and 07 for Dmen but we should look at how the league were different and the strengths and weaknesses of any player in either era to make a more fair comp.
There is always the "the best are always the best" arguments as well but shouldn't we also account for greater chance of variance in a 30 team league than say in a 6 team league? (In terms of more competition for top 5,10 scoring ect...)
On a final note each season is indeed different but we also have to look at the style of play and the forwards in the league for Dman comps not just the other Dmen IMO.
Harvey for instance wasn't a dominant offensive Dman on the surface but we ahve seen clips of his rushing ability and maybe he is more a product of his era rather than "not being able to dominate offensively."
When I have more time I will do more research for the entire NHL history on scoring levels for Dmen in the NHL and how they relate to overall scoring leaders as well.
Frankly I was surprised to see how well Lidstrom did in context as I viewed him more as a consistent steady D-first type of guy but his offense was more impressive than I thought it would be.