I don't believe the issue (at least as far as I know) has ever been Left's arm strength. I don't even think there's been a big hoopla over his accuracy either. His issue is and will always be his ability to see through his offensive line. He can't see over them, so he needs passing lanes. It's hard to create passing lanes when the line can't hold their pass blocking assignments. Lastly, the offense he's running isn't conducive for a QB with his limitations to be productive. Having him take the bulk of his snaps under center with five and seven step drops is absurd. That gives the defensive front a chance to get pressure, but more, get their hands up when he tries to throw. Even taking a three step drop is even more difficult.
Again, I'm not an unabashed proponent of the spread, but I'm not a hater of it as well. It works for numerous reasons and I believe had Kugler and Higgins used the spread, Left and the offense would be more successful in it.