Some truth there, but not really. When I've watched NHL games from the 1950s or 1960s (admittedly I don't do this often), I often see creative offensive plays that are still standard today such as a forward circling the net, going back to the point, hitting the late man, etc. These aren't things the Soviets invented. Bobby Orr's presence had already started a big change in the N.A. game long before 1972. And the WHA's existence from that same year started the era of players pursuing big money as professionals (which you refer to later).
Yes, and this factor is always unrepresented in these discussions. When the average salary of a position goes from $80,000 a year to $2,000,000 a year in about 15 years, there's going to be A LOT more competition for the high-end positions.
As has been shown on here in several posts before, the guys who were born in about 1960 or later aged extremely well. It's the guys who were born in the early 1950s to mid-1950s who aged extremely poorly.
Think of some players who started (at young ages, say 18-20) between 1979-80 and 1982-83: Bourque, Messier, Gretzky, Ciccarelli, Stevens, Moog, Coffey, Murphy, N. Broten, Carbonneau, Brent Sutter, Francis, Hawerchuk, MacInnis, Vernon, Nicholls, Vanbiesbrouck, Andreychuk, Housley, Verbeek. All of these guys were still big-impact players well into the 1990s, some until the end of the 1990s, and a few (Messier, MacInnis, Bourque, Stevens) well into the 2000s.
That's going forward, say, 13 to 22 years from their debut. But go back and look at players born from around 1950 to 1958 and see how many were still big-impact players from 1983 to 1992. If they weren't already gone by the early 1980s, most of them flamed out quickly by 1985 or so. Basically nobody was a high-impact player anymore by the mid-1980s... or even the early 1980s (maybe Brad Park and a couple others).