There is a LOT of bad QB play in the NFL. This is why the McCown's, Gabberts, McCoy, Dobbs, etc, etc, etc hang around forever and get multiple opportunities to be the guy before moving into permanent journeyman role. Which, even then, from the lack of QBs coming out of college who can hack it at all, they have steady employment.
I get the frustration. But Kyler could do really well on a lot of other teams. Imagine if he was the Dallas QB. He would be just fine. I don't think they would even miss Prescott.