As far as passing yards go, with the team set up to run Zeke, no matter how good Dak is he's not going to throw for a bunch of yards. Aikman threw for over 20 tds one time in 12 years. In two SB years, 1993 and 1995, he threw only 15 and 16. His last 3 years, without a great team around him, his completion %age was under 60, despite having years and years of experience.
Some of those numbers, like rating, are tied in part with touchdowns and yards, again, with a running offense Dak won't have the attempts to get lots of touchdowns and yards.
Certainly Dak needs to improve, but even if starts hitting more receivers, his numbers still aren't going to be sparkling....