Transfers are one of the biggest ways to change a club's fortunes. Look at Everton, year after year of overpaying for crap players, going nowhere.
They finally got a few transfers right with Ben Godfrey, James etc and are looking relatively decent. We on the other hand have repeatedly cocked up transfers since Poch's first two seasons. Ndombele, PEH and Regui are our only decent signings in years.
We still miss prime Rose, Walker, Jan, Toby, Eriksen, Dele, and to a lesser extent Trippier. Jose has his faults, but our transfer failings have chipped away at the foundation built in Poch's early years.