A couple of things to consider.
Someone correct me if I'm wrong, but I remember it being mentioned in 2 of the 3 game broadcasts so far, that Kiffin has changed terminology. If that's true, then the offense, and obviously the QBs are getting some on-the-job-training right now. And they are both being handled differently, I assume not so much on their grasp of the playbook, but in how quickly they can process the call and disseminate to their teammates. Therefore, we have seen that when Sims is in the game, they line up without huddling, and simultaneously he gets the call and is scanning the defense, and it is sometimes a struggle to get it all done before the play clock strikes zero. But once the play is run, execution has been great thus far through three games. He also performance excellently when they are running those first few plays of the game of 2nd half, by script. When Coker is in the game, he trots over to Kiffin to get the call directly in his ear, trots back over to a huddle, and then they run the play. Again, once the play is run, there has been more issues with Coker in execution as a team, including in his decision-making (when to get rid of the ball, etc). To me, the positive is that this will only improve with time, as they have both shown that they are more than capable. Things will start to click, with one or both. I'm looking forward to seeing Sims getting that play out quicker, and Coker hitting on more of those long throws.
Coincidentally, when DePriest, the defense QB, is not in the game, we have the same issues. In both cases, inexperience and/or youth needs to be overcome. Not everyone comes in like gangbusters, doing everything right, I've heard Coach Saban use the word 'develop' quite a lot through spring and so far this fall, and that's what these guys need to do. Sims/Coker are no McCarron between the ears, in experience, in instincts, etc yet, and that's OK. DePriest is no Mosley (he's not TOO far off), and that's OK. We can and will still win with these guys.
Why? We have the best head coach in all of college football. And we have quite possibly the best coordinator tandem in college football. We'll be OK.