CloakNNNdagger
Hall of Fame
My best guess is the following:
Mallett consistently makes good pre-snap reads and relies on that read almost 100% of the time (explaining his consistency getting rid of the ball so quickly). Therefore, once he has made that read, everything he does subsequently is with the determined intention to throw the ball to that primary read (including looking off the defense, etc..) This process can be quite successful in high school and some college systems, but if he has predetermined where the ball will go pre-snap, and he is not able to move to 2nd and 3rd progressions, the NFL will expose him. Perhaps his poor performance vs. Cincinnati was the result of the Bengal coaches have a week to prepare for him after the Cleveland game (and not simply due to an injured pectoral muscle).
Therefore, having success in relief of Hoyer (KC gameplanned for Hoyer) makes sense. Also, OBrien wanting to keep this week's starter secret would also fit into this theory.
If this is the case (and I hope it isn't), he can look very good against certain teams and in short stints. However, once teams have tape on him and begin game planning for him, they will take serious advantage of him.
I can't say that you're not somewhat correct about the possibility that he may not go through all his reads all the time. But to say that it is purposeful goes way beyond what can be seen in the history of his limited observable play. What I can say is that you do not in any way need to look further for his poor play in the Bengals game than his pectoral injury. Have you ever had a sore pec, simply from lifting weights, then a day or two later tried to throw a spit wad? Well, when you have even a fairly small tear of the pec muscle, you can experience excruciating pain when throwing that spit wad, with less accuracy. Then, with a completely ruptured pec (as was in the case of Mallet) to the excruciating pain and the lessening of the accuracy, you can escalate that to loss of accuracy and lack of velocity, resulting in total inability to do whatever you intended to do with your passes.