Your question wasn't directed at me, but I think I've got a couple responses.
RE: Year over year improvement - He's taken a massive step forward, but stats don't tell the entire story. He's went from a circa-1980's John Fox offense to a far more modern, integrated system. The way I see it is that Fox probably wanted him to move through progressions, set feet and make plays. This is the 'traditional QB' type skill set and is extremely hard to do. It makes sense that Mitch had difficult showing he could handle it in practice coming off of a North Carolina offense run by Larry Fedora, which was largely built around 11 personnel (1 RB, 1 TE, 3 WRs), did push tempo (like Chip Kelly) and had a fairly simple 3-4 concepts he was trying to implement per game. With Nagy it's far more comparable to what he's done. I'd add a lot of the pre-snap movement and reads let's Mitch know exactly where he's going ahead of time. His jump year over year can be compared to Jared Goff. Much of that jump was being in a better fitting scheme, not just the players development.
The areas where Mitch falls short appear to be ones that are hard to change. Specifically I see him struggle when the timing of a play is disrupted and he has to improvise outside of tucking and running with the ball. In that respect he's similar to Kirk Cousins. As the play breaks down and it becomes 'backyard' football his chance of hurting his team increases.
That's where I see those 'WTF' type throws that leave you scratching your head. The best way to curb that is to just get a rid of the ball when it's not there. The problem there is you want the player to stay being aggressive, so how to you promote being aggressive but also ask mid-play to shut that down and just end the play?
