Pretty easily as the regular season is more balanced for every player.
Teams advance in the playoffs not individual players and the way I tend to rate players is roughly 75,% regular season and 25,,% playoffs historically.
If you or others give more credence to playoffs than that the question I have is 2 fold.
First do you do that consistently for every comparison and 2 how do you account for say the 6 team league versus the 32 team league?
1) Your weight is off. The regular season exists to separate and organize teams for the playoffs, the point of playing professional sports is to win Championships. The regular season is for fan entertainment and to make money for players and the league. The real season starts in April.
2) Teams advance in the playoffs yes, but since Matthews entered the league the Leafs are 3rd in the league in total points over the last 8 seasons. Matthews isn't on an island out there dragging a plucky team to the post season every season. He's a superstar player on a good to very good team.
Teams advance in the playoffs, but Matthews cap % he takes up demands that he bears a proportional weight of responsibility to produce when the games matter the most and he routinely does not do this at an elite level. The team he is on suffers from his lackluster play and he plays a proportional part in why his team hasn't won more than a single game in the 2nd round.
3) I don't understand how a North American sports fan could possibly NOT give "credence to playoffs" but to answer your 2 questions...
-It's done consistently for every comparison of similar caliber players, yes. We're comparing two guys who could be potentially considered as the greatest american players of all time. We're not comparing Patrick Kane and Nick Abruzzese here.
This is a common argument and not as clever as people think it is. "Oh so Pat Maroon is a better player than Matthews then since he won 3 Cups!?" etc...It's intellectually lazy. You have to compare players based on the caliber of talent and effectiveness they've shown over their career. So comparing Kane's Stanley Cup successes and overall playoff resume is absolutely relevant if someone is going to suggest Matthews to be the greatest american player ever.
-Why on earth would we be comparing O6 players to the modern NHL with championships? Again, we're talking about Patrick Kane and Auston Matthews who are playing in a 30, 31, and 32 team league over their careers.
Team game.
Not a tennis match.
If Matthews was better his team would have better playoff results. He is a huge part of his team and his lack of effectiveness along with his high cap hit regularly weigh his team down in the playoffs. This is such a weak-minded mentality as well.
