I completely agree, you gave a good assessment of the changes over the decades. The NHL is much better today, but in my opinion, the old-time 1970's and 1980's hockey was much more entertaining.
I think that NHL players have become so good defensively (including better strategy) that the NHL should start playing entire games with only 4 skaters (as they do in regular season overtime). As good as the NHL players have become, the games have become more boring.
PS: Another difference is with skates, modern skates are built for speed whereas skates in the 1970's seemed very awkward in comparison. Even the sharpening of skates has become more consistent.