I've always felt that it's mostly (not entirely) a byproduct of the coaching staff allowing the QB's to do more in the offense. The diversity of play calls in year two for all of these guys is much greater, and they're allowed more freedom to spread the ball down the field.
Of course, there's always the fact that we drill the crap out of them over the winter in the film room, they get added reps in the Spring and Summer as the clear #1, etc. But there is something systemic in what we do that accounts for this jump, and I remember how much they opened the book up for Ell, Klein, Waters, etc. in year two. I feel that's a pretty significant variable.
I agree and its very significant.
I would guess Ertz's biggest jumps will come in YPA and TDs. Its possible, if not likely, that INT% and YPC will get slightly worse, but mostly because he will be allowed to take a few more chances and defenses will have better gameplans against him. Overall, the efficiency of the offense will go up, especially since he'll be paired with the best SO running back besides Sproles and a very good JR in Silmon. Plus a pretty good group of playmakers at WR. IMO, next year's offense is going to be really good, at least top 30 and probably top 20.
To piggy back on this I've felt in addition to calling more plays, it's also just more grasp and command of the offense. This is season is perfect microcosm of this in that through the first 4 weeks the biggest knock we had was not just play calling, but straight up execution. Tons of false starts, delays of game, and a general lack of any offense flow. It just looked like a horribly misfiring engine. But of course as the season worse on, Ertz got more comfortable, and his ability to better command the offense improved drastically, and subsequently so did the offense. I also thought that therefore the 2nd year was basically the further extension of this. The battle no longer becomes can he get the play in time, but can he read the defense properly and make a change if he sees fit, and that's simply something that you can't simulate in practice no matter how hard you try. The expansion of the playbook and better play calling therefore is more having the command down, so the play calling improvement followed. A bit of can you even walk before I tell you to run.
To bolster this you saw this in 2011 with Klein, while we still took the clock down in 2012 plenty of times, in 2011 it was nerve wracking as hell as to whether or not we could even get the play off, and would it even be an effective play in work.
Side note for _FAN, I like that chart showing the improvement, and I am guessing you just factored the average improvement of Bishop, May, Roberson et al to apply to Ertz numbers, but I personally see his running stats go down, and at the rate of Klein's did in 2012. Not necessarily a nit pick, just it stands to reason that just like Klein Ertz's improvement in the passing game will lead him to need to run less, and the emergence of Barnes and Silmon will mean he'll need to carry the ball less anyways.