Not sure we watched the same Nathan MacKinnon because, dude, what makes you think the most stubborn player in all of hockey is going to make adjustments to his crash-and-bang style? Look how long it's taking him to make adjustments in OT and knowing when to back off a puck battle--he's still struggling with that NOW.
Jarome Iginla is probably a good comparison, though IMO Iggy had more hockey sense than Nate, though Nate had more raw athleticism and talent. He lost a few steps in the latter part of his career but still had that elite shot that allowed him to still put up respectable numbers as a power play specialist. But once the strength and power really regressed and he just got pushed off the puck way too easily, it was over.
Mind you, he was thirty-nine when that finally happened, but again, I don't see Nate making adjustments to his game. He's going to be a bull in a china shop for the remainder of his career no matter what.