For what its worth, I can totally understand, why fans have lost quite a bit of hope in ETH. Some of his decisions weren't for my liking as well but that applies to Fergie as well. You'll always take the good and the bad and at the end, when the good has more weight, you're happy. This balance is really on the edge now with ETH for me personally but you also have to see the possible negative consequences.
Bringing in another manager will simply restart the situation, we would again have high hopes for the next guy (not that I really know of any suitable candidate right now), would want to give him time, would want to back him, give him a pre season, let him adjust to the club, to the league, to the players. The manager will give chances to most of the players to get to know them. Bla bla bla. So lets face it, the 1st year after a change isn't really anything to base decisions on. Maybe only because he completely fails but actually, not even that would be completely fair. To me, that is one more year added where the club doesn't really move on. There most likely wouldn't be a big clearout, there most likely wouldn't be 6 or more new additions. On top of that, lets not kid ourselves, our internal structures will not become better by switching managers. There's still no recruitment team that (as of now) really warrants trust (not yet). Same for the decision makers above.
I don't really understand, why people are quoting Rangnick about us needing big changes at a lot of places but then are in favor of hopping from one manager after the next while the rest of the structure stays as it is. I think, that is exactly not what he meant.
And while other clubs did well using such an approach, more often than not, there was an element of continuety in the organisation. There is nothing like that apparent with us right now. Which plays a role in some of the decisions that have been made in the last 1,5 years as well. Bayern is a bad example, they are miles above anybody else in their league. Just look at last season, it was as if their competitors went out of their way to hand them the title after all.
My plan would be the following: encourage ETH to stick to his principles, play the style he wants to play even when results are bad. That hopefully will help him to put players on the bench who don't do what he wants him to do and hopefully (if not nudge him) integrate younger players a little more. Sit together with DOF and make a thourough plan with multiple scenarios for next years summer. Not necessarily in terms of actual names, but in terms of profiles that are needed (skillset, age structure, budget). I completely agree that ETH should have too much say in recruitment, a healthy amount but not more. I wouldn't be shocked, if he would actually like that. From then on, recruitment will start to identify suitable targets, yadda yadda. DOF should also create a contingency plan, which manager would suit the current set of players and ideas in case everything breaks apart. The overarching narrative has to become "we are where we are because we made mistakes in the past, but we'll do our best to not repeat them".
Again, I understand that people are disappointed with ETH. But to me, I think having a suboptimal plan is better than having no plan at all. We all know that the environment in our club is a challenge in itself, chances are, that every possible manager will look worse than they did before. Only quick fix for that would be revolution but that isn't very likely. So it has to be evolution and that means streamlining decisions to a positive vision. Nothing less than what Pep tweeted about one of those days, with everybody in the club pulling in the same direction. At United, it looks more like our decision makers are looking for manager to hand over the rope, to get off their own accountability. There is one scenario that I would see as fair - switching the manager but on the same hand Murtough and everybody in the football department. I personally would add all players at or above 27 as well (not necessarily just those). Reset ok, but only a very thourough one.
fyi: I am bit suprised, that so many people give ETHs words with the Ajax comparison so much weight. I mean, it is the press, nobody knows wether that is really what he thinks or wether it is something he just says for this or that reason. To me it is obvious that he definitely had the plan to make fundamental changes, all targets indicate that plus the first couple of games last year. There are a few factors that have challenged that plan though, recruitment (I think FDJ was a very essential piece), disciplinary issues, injuries and so on. Obviously no manager can expect an easy ride but putting all issues to his name does seem a bit shortsighted as well.