It's not an overreaction. It's not even kneejerk - lots of people pointed out the obvious after that transfer window; we didn't do enough. Even Koeman knew we didn't do enough. We fell at least two, and more likely three or four players short. That lack of depth will show over the course of a season, and when you're playing a useless centre half as a left back, a young playmaker who has no consistency and a striker who doesn't belong in the league, then that shows exactly what the score is.
We have to cross our fingers that we can get through to January without a few injuries.