this is why it isn't nice for things to spoil too much in a team because fixing the same thing would be an easy stuff, we have seen how Manchester United has become I terms of their overall performance even before amorim asume office as the head coach, we have also seen how how he managed the affairs in the remaining days of last season, we saw how difficult things were for amorim so I don't expect magic to happen in the upcoming season, although we can't tell what happens then but there should be preparation from now, they should try as much as possible to get some good players just as you said, next season might be worst for them if they fail to prioritize the needful, I feel bad whenever I remember the United we use to know before, everything is just falling apart, it just look as if it can't get better soon.
It is not always about going to top, it is about growing and doing better. For example, Erik Ten Hag has a 3rd place under his wing, and even EFL and FA cup too. He still got fired, didn't he? Because that third place, didn't turn into a second place, nor a 4th place, it turned to 9th place or worse this season when he left. Meaning, it's about growing to be better, not to be at the top. Amorim doesn't need to be 3rd place next summer, he has to be 9th, that would mean improvement.
However, a year later, he has to be battling for 5th or 6th. And a year after that, battle to be in top four. That is improvement and if he does that, then great. Nobody wants him to be third place next season, impossible task, but even if he is, a year later, if the return of that third place is becoming 10th place again, then he should be fired anyways. United needs sustainable consistent improvement, not one time big score.