Point one: Slavin is as far ahead of other defenseman defensively as McDavid is of other forwards. it's worth noting that in head to head matchups, Slavin has dominated against McDavid, and is essentially the only defenseman in the league who has.
Defensive metrics are just utterly terrible across the board, most of them based on shot attempts, like the ones that claim McDavid is an average defensive player because the ratio of offensive chances he creates to defensive chances he gives up is decent. That means he's creating enough offense to outscore his defensive impact, not that he's good defensively. Slavin has also suffered in some of those metrics because he's not generating offensively, leading to Dom famously and hilariously claiming that Slavin was being carried defensively by Dougie Hamilton.
Point two: Offense is not more any valuable than defense. Giving up fewer goals than you score is how you win the game. Scoring goals and preventing them have equal value. You, and the league, have always played a much higher value on offense, because hey, it's sexy. That is an emotional response, not a rational one. Edmonton is losing games and has likely already bombed themselves out of the playoffs because they do not value defense. There should be a lesson there.
To me, this is just a really simple abstract question: Would you rather have the best offensive player in the league or the best defensive player?
