This is based on arbitrary subjectivity.
McDavid will inspire an entire generation to try and dangle very well at very high speed and that will also change the sport. Every generation there are few players that change the game.
I find very little validity at being "the first one" as it will always give an advantage to the one that was first there, which is situational and out of the player's hands. Might as well try to find out the very first player who did a one-timer. Revolutionary!
Contrarily to most, I find there are very few sports that have a clearcut #1, because you're always dealing with different eras with different dynamics and different environments (everything in and outside the sport). The more eras advances, the more the sport advances, the less space there is for revolutions to occur. Bobby Orr had the huge advantage, like Gretzky, coming at the start of great expansions, which's talent dilution magnified their talent. The disparity between the best and worst player was far greater for Gretzky and Orr, than it is for McDavid. So they had a double advantage. Being there first to revolutionize their sport, and a greater talent disparity to magnify their superiority.