I just feel like I've got to say something on the subject of bad D or G from the past observed through youtube clips or SN's top goals from X decade.
Those youtube clips are clips of "highlight reel goals". Ususally, these types of goals are the only ones left from the past as they're of course worthy of the highlight reel. No one saves a clip of a tip in, or a "normal" goal unless they're historically significant. A large majority of highlight reel goals usually occur due to bad defense/defensive breakdowns. Of course most defensive breakdowns occur due to mismatches. These clips are just like cherrypicking data. I'll show an example why.
I dont know if you guys remember that Malkin goal in 2012 against the Lightning where he just walked right past everyone. 50 years from now, some guy will see that clip and say "LOL defense was so bad back then. What a pathetic poke check attempt! What was that other guy doing standing around? Conditioning must have been a joke!" while ignoring that it was against the backup G and bottom pairing D. I mean the goaltending of old man Roloson and the defensive play of those bottom pairing defenders is totally representative of today's hockey! Same thing with those Orr clips. As you said, they were against bad players. Was the defensive play of guys like Darryl Maggs representative of the entire era? Can you show me numerous clips of Orr embarassing guys like Savard, Park, legit elite players? Not to mention that the % of Orr's points against such players is not very high.
Defensive systems back in the 70s were much more lax than today, but nowhere near as bad as is usually stereotyped thanks to the cherrypicking of clips. I bet you 30 years from now, the only goals you'll be seeing from today are goals like the Malkin goal mentioned above, the Ovechkin on the back goal, the one where McDavid blew by the two D of the CBJ, that Kadri assist this year etc. If you look closely, they all resulted from terrible D or G, and that is exactly what that guy will be looking at, not the sick dangles. Of course, his natural conclusion, since those clips are the most readily available, is that defense in the 2010s sucked ass.
Rant over.