As I recall, the issues surrounding Justin Fields that caused his fall in the draft were:
1). Work ethic - Orlovsky trashed him citing rumors that "He's a last-guy-in, first-guy-out type of quarterback"
2). Mechanics - Orlovsky (again) questioned his delivery speed. I think it was on the draft broadcast I heard him point out a loop in Justin's arm motion.
3). Reading the field - An NFL team put it out there that Justin threw to his 2nd read or later on only 7 of 225 passes.
4). Medicals - There was a late revelation that Fields takes medication for seizures.
Justin has proven himself to be a first in, last out guy, prompting an apology from Orlovsky. There are no questions about his work ethic or leadership. He's definitely tightened his mechanics, speeding up his delivery heading into camp last year. He seems to have cleaned up his footwork this year. The medical doesn't appear to be an issue as he's never suffered a seizure when taking his meds.
Reading the field is the only lingering question. Kurt Warner was very positive about that. In his breakdown, he saw Justin moving through progressions and throwing to the right read. Consensus seems to be that it's less an issue of Fields knowing what's going on and more an issue of trusting what he sees and letting it rip. Hopefully we'll see that as we get into preseason games.