I think it was "tougher" to play, and there was much more physical play, because it was an era where lot of very good forwards battled against a lot of very good defensemen, with only a handful of elite scorers who could make even those very good defensemen look bad. Very few players in the league had elite level skating, so defenders could play tighter and more physical, without worrying about getting walked, which is why size became so important. Being 20 lbs heavier than someone who can't just walk around you is very beneficial, and the ability to do something like make an outlet pass becomes less important.
Today, defenders have to contend with some of the best skaters the NHL has ever seen, and playing tight and physical would be a stupid choice. As a result, we've seen a massive shift to a league where skating and skill matters more than just size. And if I have my choice of trying to skate around Dan Girardi with elite level skating, or skate through Sam Girard with more size, I think skating around Dan Girardi is going to be much easier and more effective.