It's my impression that the guys that were considered the top defensemen in that era were all very good/great defensively. I don't think it's until after Orr that you get the offensive specialists on D that are not that great defensively.
EDIT: I'm sure there is an exception or two. I would be interested in hearing who those were.
Kelly was the leading rushing defenseman of the 1950s. But he did not shirk his defensive responsibilities in the least. In fact, in what is known as the Original 6 era, there were very few, if any, players, forwards or defensemen, who were not responsible on defense. Some were better at it than others, of course, but the point remains.
There is only one instance of defensive irresponsibility from that era that I know of. It was reported at the time that the Black Hawks became so demoralized post-war that some of the players did not care and shirked their defensive duties. But it was not because they were incapable of playing responsible defense.
Doug Harvey, a tremendous all-around athlete, was every bit as capable of rushing as Kelly, but he did not see the need to do it often since the Canadiens were so loaded on offense. He was content to play the team game, even if that meant he gained fewer points. I do not intend to diminish Kelly by saying this; rushing was just part of Kelly's nature and his game.
Kelly was regarded as the best defenseman in the league in the first part of the 1950s, over even Harvey, and would have won more Norris trophies had that award existed. I have noted on this board earlier that Harvey's game was much more subtle than Kelly's, since he wasn't as overtly spectacular, and that it took a while for observers to recognize the extent and depth of his talents, to recognize that he was actually controlling play when on the ice. By the mid-1950s, observers, including the press, almost unanimously regarded Harvey as the best defenseman in the league.
It is indisputable, I think, that Kelly got first team recognition on defense because of his rushing, because of the number of points he gained. That's not the case with Harvey, who was recognized for his all-around skills, his defensive as well as his offensive abilities and his unmatched ability to set the pace of play.
Another significant thing about Kelly was his clean play. He won the Lady Byng four times, three times as primarily a defenseman with the Red Wings and once as a center with the Leafs. That a defenseman could win the Byng and still be at the top in the league at his position was truly extraordinary. His reputation as a clean player made him all the more popular. He was widely admired for both his abilities and his sportsmanship.
It's notworthy in assesing him that Kelly was part of two dynasties with two different teams, the Red Wings of the early 1950s and the Maple Leafs of the 1960s, and at two different positions, defenseman and center. I differ with Stan Fischler on many things, but at least he was right in rating Kelly highly because of his diverse skills, which enormously increased his value to his team. Fischler, as I recall, had Kelly as high as 3rd or 4th on his all-time players list when it first came out, around 1981, I believe. That's quite a bit too high in my book, even from the perspective of 1981, and, of course, Kelly has gone down in Fischler's later all-time lists.
Another great rushing defenseman of the same era was Bill Gadsby, first with the Black Hawks and then with the Rangers and the Red Wings. He was named to three first all-star teams and four second teams, the first team selections all coming when he was with the Rangers. It was Gadsby who displaced Kelly and joined Harvey on the first team. Since Gadsby still earned a second team selection in the 1960s while with the Wings, I wonder what the Hawks might have been able to do in the early 1960s had they managed to keep Gadsby. As it was, they traded away perhaps their best player--certainly one of the very few stars they had--to the Rangers. It did them no good, while, beginning with Gadsby's second year with them, the Rangers became a playoff team for a few seasons, finishing as high as second.