I would put all the blame on Ten Hag because he is the only coach that has used a huge amount of money to buy players above their value which is affecting the club performance and financial state. All most all the players he bought are all average players who cannot withstand the pressure in the EPL competition. United bought the wrong players and expected a magic or what.
Ten Hag really made very big changes at Manchester United. His strategy was clear, he was doing the same thing he did at Ajax, buying young players and believing he could turn them into a strong team. In fact, when he was the manager of Manchester United, the team’s results were much better, and when he left, everything fell apart. You are right that the transfers he made did not deliver the expected results and the management did not want to wait any longer. And now I doubt that Amorim will be given the same transfer budget.
Regardless that Manchester United is yet to become a formidable team in the Premier League, i still applaud the efforts of Eric Ten Hag while at the club because he won the EFL Cup and the F.A Cup even when the team was struggling in the performance and if it was Ten Hag that reached the Europa League finals as Amorim did, he could have won it for Manchester United because he doesn't joke with finals. Ten Hag lavishing money on signing players to the squad was just a show of love to those players while expecting them to also reciprocate the energy but the players failed him, it wasn't his fault after all. The only mistake the management made was not sacking him earlier before he started having more problems with some of the players due to their poor performance. If a team do not align with their coach it definitely becomes a problem. Amorim may not be given a big transfer budget but if they succeed in selling some of their players, the funds will be generated from there and he use it to buy players that he prefers.