This team, the manager, and the surrounding footballing organisation were fundamentally flawed. It took the wheels coming off the wagon for this to be fully exposed which, with the subsequent suffering involved, ensured changes were made (or at least attempted, even superficially).
We have the semblance of a modern structure in place, with excellent footballing people seemingly being added (Paul Mitchell would be ideal for recruitment) and we have the most exciting 'young' manager in Europe joining in the summer, bringing with him a coaching staff and a footballing philosophy that, if not matching, at least attempts to mirror what Klopp and Pep are implementing. Our team is barely playing the same sport as Man City and Liverpool atm; Ten Hag will demand we make the attempt.
Ole, for all his positives and qualities as a person, would never have helped us close the gap. But if he, and the team, had 'played to their fullest potential this season' we would've easily secured 4th, potentially overtaking Chelsea in the process, while remaining comfortably adrift of the top 2. And comfortably adrift of the top 2 is where we would've stayed season after season. I don't think there's a single United fan who would be happy with that but the Glazers sure as shit would be. The security of Champions League football without any of the discomfort of the transformation needed to actually win the thing? The Glazer dream. It took the pain and misery of the implosion we've experienced this season, politely but unintentionally exacerbated by Ralf's inability (or refusal) to adapt to the players, to force their hand and to allow control of the club to move towards people who have football, rather than commercialism, as their primary focus.
The squad has also been exposed as not good enough, seemingly even from the perspective of caring, and Ten Hag will come in with a clean slate to do whatever he pleases, in terms of selection and transfers, without any rumbling of supporter opposition. Every single fan is ready for a comprehensive rebuild and they're happy for the manager to sacrifice whoever he wants to achieve that. We've hit rock bottom so many times performance wise this season that the term has lost its meaning. There's no curtain of PR and spin the squad can hide behind anymore because they've squandered all credibility. Ralf has, without meaning to, absorbed all the negativity and petulance the more troubled players were drumming up. I think with the benefit of hindsight he'll act as a sacrificial lamb to Ten Hag. If by December next season the team still can't press and there's press leaks of 'incompetent coaching' or 'an inability to transfer from the Eredivisie to the Premier League' emerging, who in their right mind is going to actually blame Ten Hag?
This doesn't excuse Ralf's tenure, as he has failed and proven wholly ineffective as a manager, but he clearly remains an expert on how a club should be run and what a modern team looks like. The 6 months in charge will have given him an understanding of the team that should prove invaluable in its rebuild and he'll be a brilliant confidant to Ten Hag on why/how/what/who/when etc. it went wrong; this can only increase the chances that Ten Hag gets it right.
This is probably an optimistic interpretation of events as it was most likely PR and 'saving face' that drove the organisational shift, and some of the players are still going to be whinging idiots whoever is managing them, but the motivations underlying these changes are almost trivial; we're moving in the direction of success for the first time since Ferguson retired and it wouldn't have happened without monumentally failing.