It is easier to play well when you don't have to win a la Liverpool and spurs
Moyes - qf in CL, 7th in PL, R3 in FA, semi in LC
LVG1 - no CL, 4th in PL, R6 in FA, R2 in LC
LVG2 - 3rd group in CL + R16 in EL, 5th PL, won FA, R4 in LC
Mou1 - won EL = quality for CL, 6th in PL, qf in FA, won LC
Mou2 - R16 in CL, 2nd in PL, Final in FA, R5 in LC
The team was moving in the right direction and quality additions were needed ( like Pogba and to an extent Lukaku were added in prior seasons), instead you got Fred and dalot. No CB like requested and no quality additions, but then blame the manager for team regressing.
The poor transfer basically compromised the season but Mourinho is at fault for making it worse just to make his point.
This fault primarily lies with whoever is responsible for the poor transfers. You either have lots of cash, good network/negotiations or great scouting, to add needed quality.
Best solution is for everyone top to bottom to get on same page and strike balance between cash, squad needs and expected results. Maybe DOF can help with that.
We definitely need to stop buying aged players like Sanchez and Matic (unless coming for cheap), as they don't last long enough to be meaningful investments at this point. Doubt either will offer much next season