I don't even think it's possible in today's NHL to separate the way it was back in the 8-goals-per-game 80's.
Goals-per-game in the 1980s reached '8' only
once, and that very early in the decade (1981-82). Goals-per-game so far this season is 6. In 1979-80 it was 7, in 1982-83 it was 7.7, in 1986-87 it was 7.35. When you then factor in how much less 2nd and 3rd-line players score now (not in raw numbers, but rather as percentage of teams' total goals), it becomes even less a factor in how much 1st-line players can score. (Not to mention today's top players regularly see 3-on-3 overtime, when it's far any easier to pick up points than any situation in hockey history.)
Removing Gretzky as an obvious outlier (well, obvious to those of us who saw him play in Edmonton), this is how select seasons' top-5 point-scorers compare:
1972-73
130
104
101
100
95
1977-78
132
123
117
97
94
1982-83
124
121
118
107
107
1986-87
108
107
107
105
103
1993-94
120
112
111
107
107
2005-06
125
123
106
103
103
2018-19
128
116
110
105
100
Not seeing any differences here...
Nevertheless, my tendency is to agree with you that it's harder for players to separate themselves in "visual dominance" and in scoring-points today compared to eras of the past... but the evidence for the point-scoring part doesn't really support this.
In the 1950s, scoring was lower than today, but we saw Gordie Howe win 4 scoring titles in a row (which nobody has done now for 19 years) with 33% more points than the second-best guy, and 46% more points than the next guy who wasn't his linemate. The same holds true of Bobby Hull's goals' domination in the mid-1960s... but it isn't fantastically greater than, say, Ovechkin's goals-domination in select seasons of his career.
Even in the first half of the 1980s (1980-81 to 1984-85), if we remove Gretzky the scoring domination by leading players isn't any greater than today's scoring domination. Here's how it was then...
619
591
577
514
513
And here's how it's been the past five years (counting this season, so these raw numbers will get a bit higher 20 games from now):
458
456
454
409
404
The raw numbers are higher in that very-high scoring period of 1980-1985, but the degree of peer domination looks to me almost exactly the same... as long as we remove Gretzky from the numbers.
**********
So, then, why does it indeed seem harder for today's players to dominate at the levels players of the past could, occasionally? I think the answer is less to do with scoring levels and more to do with the revenue-sharing NHL, and the big-business the League is today. The salary-cap means there's a certain talent-leveling off across all teams. The better-managed teams will still get the better talent through development, but not to the degree they did in the past. Like, Edmonton was an extremely well-managed team in the 1980s (despite its horrendous drafts post-1981), while a team like Hartford or Vancouver or Los Angeles had extremely incompetent management for a decade or more, to a degree that would never occur today. Or, look at Montreal's system of player-development from the 1940s through 1970s -- it was heads-and-shoulders better than any other franchise's system, and that's exactly why Montreal dominated the League to an unprecedented degree in those years. Compare with the management of a club like Chicago in those years, or, obviously, the unstable franchises of the 1970s like California or Cleveland.
And why did this across-the-board organizational competence level improve so much after the mid-80s or so, continuing to the millennial era? Answer: money. There is so much more money at stake now -- for players, coaches, management, investors, team-owners -- than at any time before the 1990s, that franchises cannot afford to be incompetent (which they
could before -- the Maple Leafs were an incompetent franchise in the 1980s, often playing at AHL level, but sold out the building every night and probably generated more revenue than any other club). Not every team had that luxury -- the Canucks of the 1970s and 1980s and 1990s frequently failed to sell out the building, but since there was no revenue-sharing, nobody cared, as long as the franchise paid its dues and went to the meetings. That can't happen today. Teams have to be competitive to survive, so they can't afford to be incompetent.
So, I think that's why it's "visually" difficult to see players dominate as much today as in the past, and perhaps why it actually is more difficult. Although, as shown above, I don't think scoring levels have much to do with it. There are other reasons.