We knew about it but no one knew how much of the issues could have been managed better. The issue with ETH, is that we know that Overmars handled him well in spite of reported disagreements when he joined United he was managed by people that were seemingly more hands-off, with Leverkusen he went back to something that is closer to Ajax and they apparently decided to jettison him because he was causing issues.
I would say that now we know or it is at least very likely that ETH is the issue and that it wasn't just United executives being useless.
The sad thing about United imo, its always been the managers. It sounds weird to say, but giving the managers so much power and having them wield their authority around, should have led to more results if they were good enough.
Somehow, it got twisted to them not being supported, when all evidence shows that they were consistently backed in the market and were given time and positivity without ever really showing any output. Moyes was given a dream job with players who had won the league. Yes, they were older, but a decent manager would have been able to get much more out of that team. He didn't identify the need for defenders or a mobile midfielder to work with Carrick. The players complained about his methods. They'd seen what success looks like, and instead of hearing them, we just called them whiners. We sacked them, and got a tough disciplinarian to punish the players for the previous season. We backed LVG for every decision despite it making our squad consistently worse. Without knowing details, fans backed him against Di Maria, despite him having clear issues with south americans who express themselves in their play. Ironically, we struggled to create chances under him and played the worst football. At the end of his tenure in May 2016, we were left with the weakest team we've had. Next, we brought in Mourinho, who'd already just come off the back of a terrible season. He bought expensive and poorly. Under him, we struggled to play out of the back or press, as he didn't adapt to the modern game. As a club, United also had a weird affinity with young players who hadn't really proved anything. Mourinho was right to question Martial and Rashford, which is why he got Alexis. Did Alexis Sanchez succeed? No. But it was clear that what we had on the flanks was not good enough. We then moved on to Ole. Ole tried, but he was not good enough long term. The lack of urgency to start seasons was a sign of his inexperience. He could not adapt to a more attacking style, despite getting relative success from the team. ETH was another manager who came in and was immediately backed. He got to punish players at will and it was somehow seen as strength. His transfers were woeful and cost the club millions. His tactics were terrible, did not suit the league, yet he was treated like a genius who just happened to take on a poisoned chalice.
My point here is that the job was never a poisoned chalice. We just always picked wrongly and felt the need to back that choice despite what we were seeing. Over time, the standards kept dropping, due to being ok with what these poor managers were producing. Mourinho and Ole are the only ones who actually tried, and they both had poor squads to work with. I think more than anything, the decisions of who the managers were going to be, were the biggest failing of the club. Blaming the Glazers or INEOS has never been the solution, and actually distracts from it, despite their culpability. Money was provided, it was used poorly by poor managers with poor tactics. For me, you blame the club, when they sell desired players and leave the manager with a poorer squad than they inherited. United have always struggled in sales, so that's never been the issue.