The issue is that people are coming out of the woodwork to harp on his shortcomings, and glossing over the point you yourself make "he’s a great defenseman because of his overall impact"
Isn't my team outchancing and outscoring the opposition, ultimately the end goal of what we are trying to do here? If they do that overwhelmingly when a given player is on the ice, across competition, yes even in the playoffs, shouldn't that ultimately be the largest part of player evaluation?
The culture of this sport is obsessed with physical characteristics, size and strength in the corners and netfront particularly, dating back to the 70s with the Summit Series and the Broadstreet Bullies. These characteristics have been the defining branding of 'Canadian hockey' in contrast to 'European hockey' for 50+ years. This distinction has been passed down from generation to generation through the hockey media, youth hockey coaches, and fan to fan. Given that being a former player raised in this culture is the surest way into NHL coaching, management, and media positions, this narrative continues to be dominant to this day, and seeps into all decision making.
And before you mistake me - I'm not saying it's a false bias, or grounded in untruths. The idea that size and strength presents and advantage in many areas of NHL hockey IS correct. However it is far too often used as a primary consideration when evaluating a player's effectiveness, usually via the eye test. "Fox looks slow" "Fox lost his man in front of the net again" "Wow Fox got pushed around the the corner" "The game is moving too fast for this guy" is all we seem to hear from certain posters. If his net results are still good, how much should we care? Are these perceived issues a predictor of future results, or a blow to our own ego i.e. how could he be that good, if I think he looks so slow and weak?
