The profit made is living off the past, and so is the elite in elite club and that started before SAF retired. The last title was squeezed out at the expense of leaving a squad that needed renewal in a lot of positions. To be fair the decline of Van Persie and Rooney was a bit unlucky, but at the age Van Persie was signed it wasn't a signing that reflects a long term vision and the fact that SAF needed Giggs and Scholes who were nearing 40 should have been worrying anyway.
So there were going to be a few not very successful years in which the squad had to be rebuild, that's nothing an elite club can't cope with, but it has to be done within a few years, and his to be done well. That's were the more fundamental problems appear:
- There is no United way in the style of football and the way players are chosen and signed. Every elite club needs it's own way of doing things, that can't just change radically with the sacking of a manager. An elite club picks a manager that suits more or less the way the club wants to play, and an elite club has a steady policy in signings, what kind of age, what kind of prices, how many academy players etc.. United's way was SAF's way, and after he retired there's no way, no direction, nothing to hold on to, it's fully up the manager, who is almost by definition someone who will leave in a few years.
- After so many years of success, the fans are spoiled. They don't have the stomach for a rebuild, even if there was a direction the club was heading in, they can't take a transition, they don't have the patience, can't endure a difficult season and then you need a very strong chairman and a very strong manager and even mentally very strong players to perform well during the rebuild with a complaining crowd. Filling a big part of the stadium with well paying tourists doesn't help either, but the pressure doesn't come from the stands only.
The second fundamental problem will resolve itself eventually with even more disappointing seasons, and the first fundamental problem will probably get adressed with more urgeny when things keep going bad. The issue is that the longer it takes to solve both fundamental problems, the longer the way back to a real elite club will turn out to be. And if United keeps lingering around 5th place for too long, the elite money will become less elite quite quickly. So the future doesn't look very bright at all, unless Mourinho starts performing well very soon. He's not the rebuilding kind and will not define a Manchester United way, but if his spending and his style pay off than it stabilizes the situation and the club can postpone defining a United way and preparing for the rebuild until he's in his last season.