Blokes mad at Mack winning is comical. This is the one award where it's not some slob of a reporter that's voting. It's voted by their own peers, other players voted and the vast majority agreed on Nathan MacKinnon. That is end of story there.
NHL players vote for this, so that means their own peers feel those 3 were the finalists. You know, the blokes these players play against, with, etc.
You are putting way too much value on the player's ability to judge other players.
Their main skillset is playing hockey, not judging how good others are at playing hockey, otherwise there would be a whole lot more coaches and scouts who were great hockey players.
Then there is the issue that the majority of players would neither have the time nor the interest to actively follow what other teams are doing throughout the entire season. They wouldn't be oblivious to it, and certainly have match preparations teach them about upcoming opponents, but they have way to much on their plate to focus on what specific players are doing. Unlike those whose job it is to follow the league.
Players can have a unique view on things that those outside cannot have, but they are anything but the ultimate judge.
Which isn't to say that MacKinnon and Kucherov weren't a given. With McDavid not being quite himself and missing some games with injuries as well, they were the clear cut front-runners, and either one would have been a fine winner.