I think there are two layers to the NW loss.
1) the first is allowing a comeback of that magnitude. It happens and like you said, first time in Fleck’s tenure we’ve had that type of loss. It sucks, but it is what it is.
2) The NW game is not an outlier. It seems yearly we lose to an opponent that we are heavy favorites against. I don’t remember the point spreads of the games, but Bowling Green, Maryland a few years ago, Purdue last year. I know we were 20 point favorites in the NW and BG games - my memory sucks but I want to say we were close to 30 point favorites vs BG. To me it isn’t the loss to NW. it is the trend of losing to teams you in theory are far superior to.
I’m not saying fire him, but I can at least understand the people that are saying it. It not an emotional or dramatic reaction to one loss. It’s a culmination of Flecks style. It wins a lot of games but at the same time, it keeps a lot of games close and in close games anything can happen.