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.
Ten Hag cannot be blamed entirely, in my opinion Manchester United management is also responsible for Manchester United's current slump.
Manchester United management decided to trust Ten Hag and also fully support Ten Hag by spending a lot of money and now they have to be responsible for all of that.
Now of course it is a tough task for Amorin to be able to fix all of this, I am also not sure Manchester United management will spend a lot of money again but they also have to be observant in making changes in the team even though they cannot change significantly at least there is a little change and progress to be better.