To me, the majority of blame lies with OGS for this transfer window. I think he's done worse than Moyes did.
Ushering out Fellaini, letting Herrera go, Getting rid of Lukaku, renewing Mata and Jones [and possibly Martial], these are all 100% on him. He's let useful players go without replacing them, and resigned useless ones.
As are his transfer priorities.
One by one:
Fellaini whilst not a world beater was a useful player, and certainly gave more for the shirt than others. Yet OGS unceremoniously dumped him to lay down the law and show he was his own man. He's not a world beater, but as an AM/2nd Striker, he'd have done far better than Mata or Lingard, as well as providing midfield cover.
Herrera, if you don't intend to replace, give him the wage you've asked for. Especially after getting rid of Fellaini and question marks over Pogba's future. He's left our midfield so threadbare that it's nothing short of criminal.
Mata and Jones: Useless players. Renew them and they take up a squad spot. Also tells the board that we have players for those positions, and they aren't a priority to replace.
Lukaku: I think he needed to go, but not having a replacement is again criminal. Putting pressure on kids like Greenwood to perform is Mourinho level cnutishness, and suddenly expecting Martial and Rashford to be consistently good is like playing the lottery with our season.
Signing a right back: Good, we needed one.
Signing a centre back: ???? We have about 5. Perhaps they aren't good enough, but no centre back ever will be given the gaping hole in our midfield. If you expose the defence, they will concede.
Daniel James: ??? I guess a cheap punt, but should be nowhere near the first team or counted on for the season.
Overall, he's weakened our squad. Badly. He's lucky that we have McTominay, Greenwood, and Gomes breaking through, but is being cruel and mismanaging them by relying on them.