I've never actually bought this argument for the older players (pre-1930s) because of the other contributing factors to their scoring - limited rosters and 50+ minutes of TOI.
Take Joe Malone's 17-18 season:
Pts Rank | Name | Year | Team | Games | Goals | Assists | Points | Team GF | LA GF | % LA | G% | P% | Avg VsX |
1 | Joe Malone | 17-18 | MTL | 20 | 44 | 4 | 48 | 115 | 105 | 1.095 | 0.383 | 0.417 | 104.28 |
If you convert that to last year's scoring level, a league average of 258, that is the equivalent of 108 goals, 10 assists, 118 points, which is obviously an absurd line. However, in terms of P%, that season is completely in line with this one 100 years later.
Pts Rank | Name | Year | Team | Games | Goals | Assists | Points | Team GF | LA GF | % LA | G% | P% | Avg VsX |
4 | David Pastrnak | 19-20 | BOS | 70 | 48 | 47 | 95 | 227 | 208 | 1.091 | 0.211 | 0.419 | 104.19 |
That converts to 60+58=118 in 22-23, which is likely around what Joe Malone's season would've looked like in a modern context. 38% of his team's goals gets reduced down to 21%, and replaced with assists.
By my metric, Morenz's season slots just above McDavid's 22-23, and below Gretzky's 86-87 as the 9th best ever season, though it isn't really near either of them - the ~6.7 total gap (3.5 above, 3.2 below) is the largest gap in the entire database. By the time you make it past the top 1% of seasons, total gaps basically never reach 1. His year in last year's scoring would be 101+55=156, which again is absurd in the G/A ratio, but 156/153 in point totals is about what we should be expecting in comparison to McDavid's year.
Pts Rank | Name | Year | Team | Games | Goals | Assists | Points | Team GF | LA GF | % LA | G% | P% | Avg VsX |
1 | Wayne Gretzky | 86-87 | EDM | 79 | 62 | 121 | 183 | 372 | 294 | 1.265 | 0.167 | 0.492 | 141.99 |
1 | Howie Morenz | 27-28 | MTL | 43 | 33 | 18 | 51 | 116 | 84 | 1.381 | 0.284 | 0.440 | 138.50 |
1 | Connor McDavid | 22-23 | EDM | 82 | 64 | 89 | 153 | 325 | 258 | 1.260 | 0.197 | 0.471 | 135.28 |
The Morenz season is a bit different, but also the same. Morenz got points on 44% of Montreal's goals, around the same as many other elite years, but his 28% of goals is matched by like just 2-3 modern seasons. However, the biggest outlier is that the Habs scored 38% more goals than league average. That's what turns it into an outlier season. If you reduced their goals to league average, Morenz's season becomes 24+13=37, or nearly the exact year both Boucher and Hay had that season. In terms of finagling with my metric, messing with league average is the aspect I've worked most on, P% really hasn't changed in 100 years (G% has to an extent, but as mentioned above that's mostly a function of the expansion of rosters and the reduction of forward TOI).