All of those figures imply that the purchases were successes which they mostly haven't been. Going through those seasons who has improved us as a team to the point where they are still a useful part of our squad today.
2014 - Di Maria (been and gone), Shaw (failure/last chance), Herrera (decent squad option), Rojo (ok as backup but injury prone), Blind (been and gone), Falcao (disaster).
So 1/6 reasonably successful signing out of that summer spend.
2015 - Martial (juries out), Schneiderlin (been and gone), Depay (been and gone), Darmian (failure), Schweinsteiger (crocked and gone), Romero (success)
So 1 or 2 success out of 6 purchases.
2016 - Pogba (mostly a success), Mkhi (been and gone), Bailly (good player but injury prone), Ibra (success but short-term and gone)
2017 - Matic (success), Lukaku (success and improving), Lindelof (juries out), Sanchez (juries out)
So all that investment and yet so few players have improved our team that we are still playing catchup. What's interesting is that on the whole Mourinho's signings seem like they are more successful. All this penny pinching this year does seem odd considering the amount of money recouped selling Depay, Schneiderlin, Di Maria, Blind etc.