I think the point of the OP is that, at some point, something's gotta give. People who genuinely believe that Rashford will accept a renewal on his current wages live in La-La Land. Or that De Gea will be fine with a reduced offer. This isn't how high-paying jobs work. You pay for someone's commitment according to the tone you have already set. If we believe that Rashford is the way forward, he will receive an offer close to the money Sancho is getting. Because that's how much we value our starting winger. Similarly, DDG didn't win the lottery. He's the best paid keeper in the world because the club believes he's the best keeper in the world. Shaw already earns more than the likes of TAA, Robertson, Trippier, and about the same as Cancelo and James. An improved offer will probably make him the best-paid Fullback in the country.
So, OK, we want to keep them because it's too big a job to overhaul the whole squad. This isn't a problem in itself. It becomes one when you want long-term commitment from your players. The infamous "United Tax" is something we're willing to pay because we believe we have found a solution to a certain problem. Leicester didn't "take us to the cleaners" for Maguire. They were clear from day one that he's not for sale. But we actually thought that we had found the leader of our defence for the foreseeable in Harry Maguire. And when you think like that and you want to acquire his services for the next 5-6 years, you have to pay high wages.
Maguire is an easy example because his stock is at an all-time low at the moment. The same applies to the likes of Martial, Rashford and Shaw. When did we put the former two on a combined half a million p/w salary? 2019? Has it paid off, can we say that it was money well-spent? The fact that we're praying to the gods of rain for Martial to stay fit underlines our poor choices more than anything else. Martial was, is, and probably will remain one of the most inconsistent and injury-prone high-earners in football. Shaw has been here since what feels like forever. He's had, what, 1 1/2 good seasons? Sure, make him one of the best-paid FBs in the world. Just keep him "motivated". Judging by what we've witnessed from him in the past, what could possibly go wrong?
In the end, ETH may prove to be our guy for the next decade or so. Maybe he'll transform the side in ways we can't even imagine and achieve wonders with these players, I sincerely hope so because, to tell you the truth, i'm tired. Not of not winning trophies, but of watching us move from one dead-end to another in terms of style and purpose. But if we're doing things wrong and the wage structure needs to be fixed, we'll be forced to make these calls.
And if that's the case, we should do it at the beginning of a manager's tenure and give him some rope. Not when everybody will be fed up with him and will start siding with the (same) players, who will be moaning... again.