I'm sure I'm in the minority but, assuming his injured shoulder is 100%, I believe 99% of Brock's misfortunes originate between his ears. He's got physical ability, enough to be an effective QB. He just doesn't process info quickly enough (right now, anyway) and trust that his read/instincts are correct, so he plays very hesitantly. For good reason, doesn't trust his OL so rarely makes it to the 2nd or 3rd progression. Stares down his primary way too often, again, a mental thing, not physical. If the primary option is not immediately open, he pulls it down and runs, typically, into the rush rather than away from it. Waits too long to throw to an open receiver, not trusting what he's seeing. All of these problems should be able to be coached out of him. I don't think he's a hopeless case and I believe he's redeemable with the proper mental coaching, film study, etc.
For now, Boley looks more poised, reads the defense quicker which results in balls coming out faster, etc. Now, he took a couple of really bad sacks Saturday, avoided one where he kept fading back and back and back, missed a couple of RPO reads, etc. But, he stood in the pocket, more times than not threw to the correct receiver on time, maintained his eyes down the field even when scrambling, etc. He gives us the best chance to win Saturday and should start. No more QB merry go round. Put him in there and let him do his thing. If he gets banged up, then Brock needs to be ready.