Poor offensive lines can destroy quarterbacks. And sometimes they never recover. I know many here chastise and ridicule the Kyle Boller years, but he had a terrible line when he was here. You could tell he was expecting to get hit on every play. He also started getting happy feet, instead of firmly planting. By then he was done.
If he had a great offensive line we may be talking differently about him; then again, maybe not.
My point is this. The OL is just as important as the quarterback when plays are developed/executed. Both need to do their jobs effectively to make the plays work. If the line fails, the defense gets more batted balls and more licks on the quarterback. Eventually the quarterback loses confidence in the line and goes in survivor mode, concentrating more on the players coming at him than the receivers downfield.