As an Oilers fan, who watches McDavid every night, I'll say this; In the regular season, no one is even close to McDavid. His separation from the rest of the pack is Gretzky-like, and can do things in the offensive zone that I have never seen any hockey player do or even attempt. The combination of speed, hockey IQ and stick mastery results in the most electrifying player since Mario Lemieux.
In the playoffs, we've only seen him play 3 series, in a 6 year span, so it is kind of hard to gauge what he's capable of in a deep playoff run. That being said, there was a poll in the Oilers threads after game 4 of the Jets sweep, titled who are you disappointed in the most for playoff performance? McDavid received almost half of the votes (of a poll with over 12 choices), by far the #1 choice (@ 45%, with Dave Tippett finishing 2nd @ 16%), and it was warranted.
The playoffs, everyone has to be on the same page, synchronized, and almost robotic like. Finishing your checks, back checking, forechecking, sacrifice, shot blocking and any aspect of a complete 200 foot game. It's pretty obvious he needs major work on his defensive zone game, including his faceoffs. He was ghosted in game 1 and 2, and it almost seemed easy for them to do it. Everyone saw the McDavid giveaway in 3OT in game 4 that ultimately sealed their fate.
We haven't seen him dominate a series yet, not even close to what MacKinnon has done time and time again.
MacKinnon is a God in the post-season. He's been in the playoffs 5 times in his NHL career and his worst playoff performance was being a point per game player (2018 6 pts in 6 games). Even in his rookie season, he had 10 pts in the 7 games they played in April 2014. Last season he was on pace to finish in the top 20 all time in playoff points, would he have made it to the finals.
Now, history could be in the making; he's at 2.40 pts per game! If we assume they go to the finals, and he plays 20 games altogether in the 2021 playoffs, maintaining that 2.40 pts/game, he would finish with 48 pts, and break Gretzky's record of most pts in a playoff season with 47 pts. Gretzky. He can break the Great One's record, and possibly win the Conn Smythe and Stanley Cup along with it. That is absolutely legendary. We are seeing a master of the game manifest into his prime, and what a sight to behold.
Now, Connor McDavid is also only 24 years old, and literally every single season he has gotten better. I hope he does get criticized heavily in the summer, and that he takes it to heart. And that we see a more complete well rounded Connor McDavid next time he's in the playoffs. He has unlimited potential and could also manifest into a legendary playoff performer.
But as of right now, Nathan MacKinnon, imo, is indeed the best well rounded player in the NHL