I don't think he's terrible, for the record. I think he's a good QB - and I don't know if Rettig would be any better, to be honest.
What I don't understand is some strange things in the playcalling.
The deep ball is a very rare thing, and that's odd. We have Carroo, who is a superstar WR and established deep threat. We have Agudosi, who is a 6'6" long body with speed. We have Grant, who can very likely get a step on about any CB on a fly route. We have Patton, who's another big body. Yet.... we don't put balls up for our WRs to come down with deep. Lots of deep ball tools in the toolbox, but we don't use them.
Even stranger is the idea that Carroo/Agudosi is an either/or concept. Why don't we have both of them on the field at the same time? Knowing Carroo is a superstar, why aren't we trying to work Agudosi in with him, rather than keeping him on the bench? Is having two deep threats in the game at the same time out of the playbook because it doesn't leave us with enough short range options?
So.... is this on McDaniels just being unable to run an offense that stretches the field? Is it Laviano checking out of deep plays at the line? Is it McDaniels not calling deep plays because he has less confidence in his QB's ability to deliver those balls? Is it something else?
It's obvious the impact of not taking shots down field, though. We limit our big play potential. We let the defenses cheat into the <15 yard range, which makes it harder to throw short passes and slants, and lets the defense get there faster when we throw to the flat. It limits the playbook on third and long (throwing <10 yards when it's 3rd and 15+ means you've already decided to punt, and are just looking for some better field position.)
So again.... Why? Is it some lacking on the part of Laviano, or some lacking on the part of McDaniels? Because it's obvious that it's a lacking on the part of our offense as a whole.