The team is better with him than without him of course in a vacuum, but that's not the issue.
Without him... What assets could you be getting back for him? And what else could you be doing with those dollars?
What if you could trade him for a solid top four defenseman and two 'high-ish' prospects. Maybe that top 4 defenseman is making half of what you're paying WN. Of course I don't know who's available, but something like that is not out of the question now. Why might that be good?
You get a top four defenseman. And you replace WN with a guy Who isn't as good but is making a lot less. Maybe that new guy plus a adequate defenseman is better than WM without that adequate defenseman.
Oh and why would two prospects be important if available? You could have NHL ready guys ready to step in the lineup in one or two years that are low cost, cost controlled... To offset what you're paying your other high priced guys.
I'm not taking the other side of the argument that signing him to that deal was a definite mistake and the club was dumb for doing it.... I'm just saying that saying they're better off with him than without him isn't the issue... It's what can you do with that money in addition to what could he get back in a trade that the comparison must be made to.