The lack of a proper DOF doesn't excuse the performance on the field in case of Eth, because he has been given a free reign in terms of the targets. Managers in other clubs would kill for $400M for their targets. Yes everyone agrees that its gross mismanagement by the club, but that is no excuse. If say, Eth didnt get the players he wanted and Mount, holjund and Onana were forced on him, then it can be a valid justification.
In a scenario where we have a competent DOF, and they said no to the summer signings because they believed they are not worth it and got him alternatives, lets say Ziyech, Raya and Watkins. What if we still played like how we have, wouldnt the fans go, "Well the DOF is shite, if Eth had gotten the players he needed, we would play well"??
Yes, we desperately need a change above the manager, Nobody would disagree. But for me and many others, the point is there is no reason to believe that under a better management, Eth would succeed, because he is not able to get the best out his very own signings, yet we are expected to believe that he will somehow get the best out of players selected for him. It may have worked in Ajax, but there were also a myriad of factors that coudl have contributed as well. Its the same a claiming, Jose had won the PL with Chelsea, so there is no reason he could fail here.