Actually, you can coach accuracy. You can't coach size & speed!
Look at TB. When he first got here, his mechanics and footwork were not that good. He released the ball too low just about helmet high, or slightly over. His stance was too wide which negated the use of his legs and hips for the deep throws and when he needed to drill one in there. Lots of dual threat guys have poor mechanics and footwork in the pocket. But, when you are scrambling and a threat to run, you can often find wide open receivers, which doesn't require as much accuracy.
When I had a chance to talk to Jay Johnson after TB's arrival, I mentioned his release point and footwork. Jay told me they were already working on these things and his improvement was obvious after his redshirt season. After he broke his wrist at SoAl, his release point dropped again due to that injury. I was coached by Larry Zeno (twice All-American at UCLA) and he changed my release point as well. The higher you release the football, the more accurate you become because you are more inline with your sight-line. It takes quite a bit of hand strength to release the ball high, because you have to pull it down to spin it. But, the higher release increases velocity and enables you to throw the ball on a line, a longer distance and helps keep the batted passes down as well.
IMO, Jennings has very nice mechanics and good footwork. He elevates our QB position. I know JD will be upset if he doesn't start or loses playing time, but I say, let the best man win!
Check out this video. https://www.youtube.com/watch?v=3ufwFzyCSzs