Do they? Who would you identify, of the players who cost a bit of money and didn't get sold on for what we paid or more, did the scouts get badly wrong? I reckon it's these:
Disaster: Mangala, Philips, Mendy (hardly the scouts fault), Bony, Jovetic (due to injury)
Never good enough: Sinclair, Rodwell, Gomez, Angelino, Nastasic, Garcia
Underwhelming: Nunes, Fernando, Navas, Torres, Grealish (for the money), Danilo, Nolito
For my money (and I might have forgotten a couple) that's all of shite signings since the infamously terrible transfer window of in the 12/13 season. And even some of these played an important role at times. The rags would manage that level of failure in a couple of transfer windows.