The McDavid for/against argument regarding Even Strength results (plus/minus, basically) is interesting. I can see legit arguments both ways.
I will say that I don't think Mario Lemieux in general (or post-prime Gretzky, for obvious reasons) are good standards of excellence in plus/minus. It was noted that Lemieux was +41 in his great 1988-89 season on a leaky team. That does sound good (and is), but Lemieux also had 120 scoring points at evens or short-handed that season, on a club that scored 347 goals. He was on the ice for 103 ES/SH goals against, which is a lot. (McDavid is currently pacing to be on ice for 87 such goals-against this season, which, given era differences, is probably about the same.) Don't get me wrong, Lemieux's +41 that season is still very, very good, as is (of course) his +55 (in only sixty games!) in 1992-93. But outside of those two seasons, he was just... okay at evens, never dominant at all. Really, in sum, Lemieux had one complete season where he was dominant at even strength.
As of today, after nearly eight regular seasons, McDavid sits at +15 per 82 games in his career. For Mario, after eight regular seasons, he was +8 per 82 games in his career. (McDavid +38 per 82 in the playoffs, Lemieux +32, and that included TWO Stanley Cups.) I don't state this with any judgement meant, as it was "easier" to score higher pluses and lower minuses in Lemieux's first-half of career than subsequently, but if the argument is that Lemieux had a peak even strength dominance greater than McDavid's after eight seasons, I don't see it, and also we obviously need to wait a few more years to judge McDavid against Mario's post-1992 career.
Overall, since McDavid's second season (his first full season), he is handily first in ES points, by a margin of 96 points over the next non-teammate (Draisaitl is actually second and is still 88 behind McDavid in more games played).
But one thing I do find a bit odd is how McDavid---still very much in his physical prime---became less dominant scoring at ES after he was 21 or 22 years old. At 20 and 21, he completely dominated the League at ES. Mario Lemieux never did so at that age (in fact, he only occasionally did so later at his peak). Gretzky did so by enormous margins for his first 12 years, but then, as many players do after their physical primes end, he fell off and depended much more on PP scoring from age 30-31 onward.
Having watched the Oilers through McDavid's career, my feeling is that McDavid killed himself (so to speak) to score at ES circa 2016-2019, only to mostly see the team fall flat. Their PP started going supernova around midway through 2019-20, which is also when the team re-entered the playoff picture. As with Mario on the late-80s Penguins, the Oilers the past few years have probably consciously realized that their PP is their best chance to win, even if this is somewhat unsustainable in the playoffs. But, as we all saw last spring, McDavid still had that "5th gear" at ES when he needs it.
Finally, let's remember that plus/minus is always 80% dependent on players on the ice besides the player we're talking about. I mean, Kucherov is -3 right now. What's his excuse?