that's on point. I have made similar argument and I am called a Dak Hater....his mechanics need improvement. there is no questions or doubts. even most Dak fanatics admit that. and you hit the nail on the head, because of his mechanics, he doesn't trust himself to make some of the throws and thus holds on to the ball too long to have the WR open before he tries to speed throw it in there. he doesn't quite have all the touch and throws....and once he improves his mechanics, then he may trust himself more and make some of the throws.....
the one thing that he has to get over is throwing with anticipation, right now he waits until the WR is looking at him or wide open and finished his route before he throws, where as mentally he has to learn to throw with anticipation to a spot and expect his WR to get or be open. Something Romo and Aikman did really well. That's why Romo-Dez combination worked well, but Dak and Dez didn't really click.
so once his mechanics improve, the next hurdle is to throw with more anticipation and trust his arm and throw to spots.
the one issue that may also improve if the above two happens is less sacks, he holds on to the ball too long which leads to a lot of sacks, if he throws quicker, then less sacks. his pocket awareness is not that great and not sure if the above two will help that....that's something totally different....but putting him in a position to throw quicker, will help that....