Trey has been part of multiple training camps and has had multiple years of NFL coaching and has had the time and means to employ professional trainers to improve, so yes Trey should be expected to perform better than them. At this point he should look much better than he does, instead of flashes, there should be more consistency and a better grasp of the basics.
Another way to look at it is too compare Trey Lance to QBs around his age. And ask how many of them have so little experience that it would take years to develop them as a reliable QB. As none of the ones drafted in the first round recently has had so many questions or doubts about their throwing ability or having the most important skillsets when it comes to what's needed to be a long time franchise QB in the NFL. Which is more than just the ability to run.
Lance being 24 doesn't completely explain why so much time should be needed to see whether or not he is the answer for the Cowboys. Of if he can really be a starting QB in the NFL. Many QBs have been able to come in and win the starting job in their rookie season and have been able to maintain their spot as a starter ever since. And even if they had their moments where they struggled or were down for a few games, they still were proven to be able to pass and throw the ball consistently enough, where there weren't full questions as to whether or not they would be able to develop their passing abilities and be a legitimate NFL QB in all of the areas that matters the most.
Lance having all of these question marks. Lives the Cowboys in a dilemma of having to decide between spending the next 2 or 3 seasons hoping that Lance can develop into a valid starting QB. Or drafting a QB who will passing ability and attribute wise, already have all of the skills and talents that some are just waiting to see if Lance can develop. As by their 4th year in the NFL, they would be way further along than Lance is right now.
