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:
[TABLE=collapse]
[TR]
[TD]Pts Rank[/TD]
[TD]Name[/TD]
[TD]Year[/TD]
[TD]Team[/TD]
[TD]Games[/TD]
[TD]Goals[/TD]
[TD]Assists[/TD]
[TD]Points[/TD]
[TD]Team GF[/TD]
[TD]LA GF[/TD]
[TD]% LA[/TD]
[TD]G%[/TD]
[TD]P%[/TD]
[TD]Avg VsX[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Joe Malone[/TD]
[TD]17-18[/TD]
[TD]MTL[/TD]
[TD]20[/TD]
[TD]44[/TD]
[TD]4[/TD]
[TD]48[/TD]
[TD]115[/TD]
[TD]105[/TD]
[TD]1.095[/TD]
[TD]0.383[/TD]
[TD]0.417[/TD]
[TD]104.28[/TD]
[/TR]
[/TABLE]
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.
[TABLE=collapse]
[TR]
[TD]Pts Rank[/TD]
[TD]Name[/TD]
[TD]Year[/TD]
[TD]Team[/TD]
[TD]Games[/TD]
[TD]Goals[/TD]
[TD]Assists[/TD]
[TD]Points[/TD]
[TD]Team GF[/TD]
[TD]LA GF[/TD]
[TD]% LA[/TD]
[TD]G%[/TD]
[TD]P%[/TD]
[TD]Avg VsX[/TD]
[/TR]
[TR]
[TD]4[/TD]
[TD]David Pastrnak[/TD]
[TD]19-20[/TD]
[TD]BOS[/TD]
[TD]70[/TD]
[TD]48[/TD]
[TD]47[/TD]
[TD]95[/TD]
[TD]227[/TD]
[TD]208[/TD]
[TD]1.091[/TD]
[TD]0.211[/TD]
[TD]0.419[/TD]
[TD]104.19[/TD]
[/TR]
[/TABLE]
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.
[TABLE=collapse]
[TR]
[TD]Pts Rank[/TD]
[TD]Name[/TD]
[TD]Year[/TD]
[TD]Team[/TD]
[TD]Games[/TD]
[TD]Goals[/TD]
[TD]Assists[/TD]
[TD]Points[/TD]
[TD]Team GF[/TD]
[TD]LA GF[/TD]
[TD]% LA[/TD]
[TD]G%[/TD]
[TD]P%[/TD]
[TD]Avg VsX[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Wayne Gretzky[/TD]
[TD]86-87[/TD]
[TD]EDM[/TD]
[TD]79[/TD]
[TD]62[/TD]
[TD]121[/TD]
[TD]183[/TD]
[TD]372[/TD]
[TD]294[/TD]
[TD]1.265[/TD]
[TD]0.167[/TD]
[TD]0.492[/TD]
[TD]141.99[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Howie Morenz[/TD]
[TD]27-28[/TD]
[TD]MTL[/TD]
[TD]43[/TD]
[TD]33[/TD]
[TD]18[/TD]
[TD]51[/TD]
[TD]116[/TD]
[TD]84[/TD]
[TD]1.381[/TD]
[TD]0.284[/TD]
[TD]0.440[/TD]
[TD]138.50[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Connor McDavid[/TD]
[TD]22-23[/TD]
[TD]EDM[/TD]
[TD]82[/TD]
[TD]64[/TD]
[TD]89[/TD]
[TD]153[/TD]
[TD]325[/TD]
[TD]258[/TD]
[TD]1.260[/TD]
[TD]0.197[/TD]
[TD]0.471[/TD]
[TD]135.28[/TD]
[/TR]
[/TABLE]
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).