I've noticed the past few years, with our draft boards being released, that we remove an awful lot of really good players (presumably for a variety of reasons, including injury, scheme, and character). It makes sense to drop players a round or two based on the severity of concern, but to remove highly gifted players from the board completely is a completely black and white way of approaching the draft and makes no sense to me.
Here are some of the rookies we didn't have on our draft board last year:
Jarvis Jones
Alec Ogletree
Matt Elam
Christine Michael
Keenan Allen
Robert Woods
Tyrann Matthieu
Sam Montgomery
Larry Warford
Many had very successful seasons.
In general (not specific to the Cowboys), it's better to draft players that you are confident in both their physical ability and mental-makeup/character. Teams can't get caught up in being worried that a player they pass on might be good. They need to focus on making picks that they believe have a high probability of being successful with their team.
They were correct about Sam Montgomery. He was cut mid-way through the season by Houston.
Everybody knew that Matthieu might be good/great, but they he also knew he might get in trouble at some point or be a bad influence on the other players. You can't judge character risk players after 1 year. You have to look back after about 3 years to see how many character risk players stayed out of trouble.
Larry Warford was not a fit in their Zone Blocking Scheme. The fact he is doing well in a man-blocking scheme is not an indicator that he could do all of the things that Cowboys wanted to do in their ZBS. It's like a 4-3 team passing a really good 3-4 NT. It wouldn't matter how good the NT becomes, that team is not going to switch schemes because 1 draft pick is available that would be great in the other scheme.
Garrett hired an outside company that specializes in evaluating the mental-makeup of players. If players don't pass their guidelines, the Cowboys take them off the board.
There will be players every year that are not on the board, but play well for another team. Drafting is about probabilities, not guarantees. You could spend 10k on lottery tickets and the upside is really high if you win, you probability is that you will lose.