It's been shown repeatedly that one Gretzky can't raise league scoring that much. Obviously you have undertaken all efforts to try and avoid using this information with your previously held beliefs but rudimentary statistical analysis makes this obvious.
It is not considered coincidental or curious as to why scoring exploded when it did. The overwhelming consensus amongst all of who have studied is that the NHL underwent rapid expansion. The 1966-67 NHL season had 6 teams, the 1979-80 NHL season had 21 teams. The League 3.5X over the course of thirteen seasons. Talent pools tend to catch up eventually as enough time goes by, but through the 80s it hadn't been allowed to settle and catch up yet. This gave high-end scorers a huge advantage because much of the league was "not NHL caliber" but suddenly were.
Imagine what would happen if the NHL suddenly had 64 NHL teams next year. The frequency with which the top scorers face a Hellebuyck or Vasilevskiy in net drops significantly. Top line players will double the rate at which they see far inferior players lined up across from them. Scoring would skyrocket.
The only people saying it's one Gretzky are the strawmen so many people seem to want to build in this thread. I only used him because he's the best example of how a single player CAN impact league wide scoring, given that he's scored the most points in a single season. Obviously, it wasn't just him, even though he had the greatest impact.
In addition to Gretzky, look at the other high end scoring talent that entered the league over a 12 year period between 1979 and 1991. Bourque, Messier, Gartner, Coffey, Kurri, Francis, MacInnis, Hawerchuk, Gilmour, Yzerman, LaFontaine, Lemieux, Hull, Sakic, Shanahan, Fleury, Jagr, Lindros, Forsberg, etc. All of these high end offensive guys made scoring look easy, and helped their lesser teammates score a lot more points than they otherwise would have, dragging scoring averages up significantly.
But then those high end offensive guys started declining and retiring, and most of them got replaced with lesser "high end" guys like Benn and Duchene and Hall and Getzlaf. The high end defensemen of that era also retired, and most of them got replaced by lesser "high end" defensemen like Phaneuf, Burns, Bouwmeester and Mike Green. Yes, there were a lot of crappy defensemen in the 80s and 90s, but there were also still a lot of pylons in the league after the lockout too. Just look at all the terrible defensemen getting regular playing time around the league. Nate Guenin, Greg Zanon, Shane Orr'Brien, Ryan O'Byrne, Matt Hunwick. Jeff Finger, etc. (and that's just from the Avs). It should have been so easy for elite scorers to put up pretty big numbers against these scrubs, but there were only 3 or 4 elite scorers in the league, and half of them struggled with injuries, so instead, we mostly got the 2nd and 3rd tier forwards playing against 2nd and 3rd tier defensemen, which resulted in fewer advantages for the offense and lower scoring overall.
And, if the league had 64 teams next year, I'd assume that the "far inferior" players on those 32 new teams would be a lot of middle-6 or bottom 6 caliber forwards and depth defensemen who would likely struggle to score much more than they would in playing defense. I wouldn't expect most/any of these teams to get an elite scorer right off the bat, so I'm not convinced that the same number of elite scorers would score enough additional points against these new teams to mitigate the 400 new mediocre scorers dragging averages down. I think the league would need to add a lot more high end talent to this 64 team league before scoring goes up too much.