So isn't it reasonable to point out that if the PP was better last year perhaps his ES production is not as high? This was the case in 16/17.
This isn't about giving him undue credit but rather framing a speculative discussion. Past offensive greats seem to have produced in all types of scenarios so why should McDavid be any different? McDavid produced despite a weak PP. This doesn't automatically mean he produces more if the PP is better. Maybe his icetime gets lowered if the PP is better and he isn't needed to be on the ice as much later in the game because the Oilers are behind. I find the assumption that you add more PP points to his ES points from last year too simplistic.
And the fact he stepped it up after the Oilers were eliminated from the playoffs cannot be ignored either. Maybe it was just timing that he really hit his stride after being sick when the Oilers were done for the year but we will never know.
Pointing out that he did not have a statistically stronger Art Ross win than he did in 16/17 should not cause any heads to be hurt.
It should when it's not the basis for the discussion yet you insist on trying to frame it that way anway, and are unwilling to consider how well underlying numbers work for future prediction, instead relying on tired tropes about stars scoring regardless, and ignoring the fact that star player scoring will routinely fluctuate and can frequently be tied to those numbers.
His ES scoring was worse in '17 because he produced fewer chances. His on-ice shooting percentage has remained the same throughout his career at a reasonable number for a player of his ability. This suggests sustainability and growth in terms of his ES play. You want to look at past players and how their ES and PP numbers frequently even out, with a spike in one often balanced by a decrease in the other, and this switching or balancing in future years. But you either ignore or are unwilling to pay attention to the fact that this can usually be seen in high percentages in one and low in the other. And career years will often show a spike in one and usual numbers in the other or spikes for both. This isn't the case for McDavid last year. His numbers suggest sustainability at even strength and and that the PP was an aberration. This is why there is a greater likelihood of him improving his numbers than most players who have put up similar uneven splits in the past. His underlying numbers suggest it was a down year. The fact he still won the Art Ross is a testament to his ability.
You bring up reasons for why he might not improve and they're valid. There is no guarantee. But the stats tell me that it's more likely he will see an increase, and that's a lot more meaningful than the same old regurgitation of potential negative scenarios from someone who so obviously has skin in the game.