I don't agree that deep ball accuracy is his issue. His deep balls to people not named Wallace were fine.
Tanny's issue is anticipation. I've got to say, he's working on it and it's slowly improving.
1) He's processing his reads quicker. It's still not quick enough, especially for the deep ball (which is exacerbated with Wallace's speed - you need to decide v. quickly to hit Wallace deep)
2) His pocket awareness is gently improving. Let's face it, it needs plenty of work but only a blind man would say he hasn't seen some improvement.
3) His anticipation of receivers routes and throwing to receivers in stride is a big issue. Sunday, I saw him hit a couple for the first time in a long while where he really led the WR to yards after catch with his placement. The nicest of those was to Hartline, sometime in the first half.
He's still an adolescent in competitive snaps terms. His ultra-calm, almost robotic demeanour is maybe misleading as to the thirst for improvement and the will to win. It's part of the reason why I'm sceptical about his ceiling being at "franchise" or "elite" level. He doesn't inspire (which is it's own problem within the team, if they feel the same way), but that doesn't mean he isn't good and progressing on the road towards very good.
He certainly hasn't plateaued. I don't think anyone could successfully argue that. The question is whether his unquestioned progress is ultimately undermined by more fundamental flaws in his QB makeup. I can't call it right now, I can only applaud him for his obvious dedication to getting better.