I think that's a bit of an exageration to be honest mate. They are frustrated, with some justification. They are the most successful club in English football, and over most of our lifetimes (or certainly mine) nobody even gets close to them.
What they don't seem to grasp though, and it's not just them, but actually this counts for very little. What you did 5/10/20 years ago doesn't matter. People around football also seem to hold to this bizarre myth about "being a winner". It's kind of played out like a very crude, working class twist on Gordon Gecko. That if you puff your chest out and tell everyone how much of a winner you are, you win. It doesn't really work like that.
If you look at say Liverpool, it was the fact John Henry did the opposite of this, and ignored the fans, that led the turnaround. He got rid of Dalglish, got rid of the bootroom, got rid of the dated culture that existed and realised it meant absolutely nothing, and actually probably just held them back. He's about as far removed fromthe archetypal "winner" that people associated, he's a quiet, weird, socially awkward nerd that likes patterns in numbers. He's very good at it.
I digress slightly. I think United probably need some ideas that are out of the ordinary. I like Roy Keane, but him banging on about "winners" doesn't really mean anything. But they also probably have to accept that most organisations are cyclical. There's no divine right to be at the top. Most businesses dont stay at the top indefinitely. There is an assumption they should, but goodness knows why, it's not common across businesses.
Ten Haag probably won't be given time. The best sort of manager they could go for is probably an Ancelotti, who manages expensively assembled rosters as well as anyone. He doesn't do the transformational long term stuff (though hes never been given the luxury of time) but he would get them organised very quickly.