You honestly believe that the scoring environment overall and/or for the elite scorers is static year after year? That when literally almost every elite scorer's PPG goes up or down in a season or over multiple seasons, that is not inidicative of something else other than individual performances?
We need to understand what the "something else" is, we need to understand why overall scoring is at different levels in different time periods.
Comparing scoring using overall scoring levels doesn't work most of the time. And comparing using dominance doesn't work either (because the quality of players you're competing against changes dramaically).
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In the 1950s, scoring is lower in the early part of the decade. Is that because defense was better and it was generally more difficult to score (than in the late '50s)? The answer is no. Just because scoring is lower, doesn't mean it's more difficult to score.
Let's compare the 1950s to the 1980s, as there are some important similarities in these decades. In both cases, there is a major influx of talent (scoring talent) unlike anything the NHL had ever seen before. Also in both cases, offense and defense both improved as the decade goes along, so the league in both the late '50s and the late '80s was stronger than early decade.
So, why then does scoring increase during the 1950s but decreases during the 1980s? This is the key to understanding.
As is always the case with scoring levels, it's a battle between offense and defense. In general, if offense wins, scoring increases. And if defense wins, scoring decreases. In the 1980s, when offense and defense are both improving, defense eventually improves more than offense, mainly because of major innovations, and great improvements in quality, in coaching. The result is scoring declines.
In the 1950s, even though, like in the '80s offense and defense both improved, the result is the opposite. Offense wins, and scoring increases. This happens partly because there is a great improvement in offensive talent and skating ability in the league, and partly because there is much smaller improvements in defense.
So, going back to Gordie Howe....he dominates scoring in the early '50s because he's competing against a very weak field. Players are generally scoring less not because it's difficult to score, but rather because talent is very low in the league....i.e. better offensive talent is always more likely to score than lesser talent.
Detroit dominates scoring in the early '50s, much like Boston in the early '70s.
I think there's very little difference in Howe's scoring between the late '50s and early '50s. The major difference that happened is the vastly improved scoring talent in the NHL in the 2nd half of the decade, led by Beliveau, Moore, Bathgate, Geoffrion, Henri Richard, but including many more. The league was a lot stronger, but Howe wasn't much different. It's just that he was no longer the best scorer.