As bad as the Catcher position has been, it takes a LOT of guys playing poorly to end up with an offense this bad. Good teams can overcome a few players not hitting, but the Cubs have more than a few. Swanson has been bad overall outside of a short hot streak. Nico hasn't hit anywhere near as well as he needs to if he is going to be the long term answer at 2B. Morel was supposed to hit enough to make up for his glove, but hasn't been hitting at all.
I don't know what makes nearly an entire offense perform below expectations, but if you listen to Steve Fifer from Milwaukee (who was on the Score last weekend), he blames Counsell and says he isn't a good offensive manager. I'm certainly not buying that a manager has that much impact and I think his assessment was more sour grapes.
Ultimately, this team's performance has to fall on Hoyer. It is simply unacceptable for any team, let alone one with the payroll of this Cubs team, to be playing such awful baseball.