Success in the NFL Draft is based on some simple principles. The best player available that fits your scheme should be the priority, especially in the first round. Drafting for need is a recipe for failing to improve your roster as much as you can and usually hinders a team in improving its roster. The Dallas Cowboys have been faithful to this, as shown by the drafting of three offensive linemen, Tyron Smith, Travis Frederick, and Zack Martin, in the space of four years. They wound up with three Pro Bowl performers who have become the foundation for their line for years to come, and the addition of La'el Collins, who would have been a first-rounder except for the bizarre circumstances he was caught up in, just fortified that unit. It applies to all positions on the roster: Take the highest graded player no matter who you already have.
Except for the quarterback. In the NFL, the quarterback position is unique. It is the one position that there are clearly not enough players of sufficient talent to go around. About half the franchises in the league do not have a viable franchise QB, and with very few exceptions, that dooms them to being on the outside looking in when the playoffs come.
The Cowboys have that franchise passer in Tony Romo, but the collapse of the team when he was injured in 2015 just reinforces how important it is to have that star player taking snaps. But Romo is racing time, and that is a race that is always lost eventually. As the inevitable day when he is no longer playing approaches, Dallas is faced with the problem of finding a replacement. If they fail to do so, they will have to try again at some point. The only thing worse than not having a viable quarterback is to have one who is just good enough to keep the team hovering around the .500 mark, where they never go anywhere in the postseason but always are stuck in the middle of the first round where the best quarterbacks are usually gone before they go on the clock. This situation has been termed "quarterback purgatory", and leaves teams with no good solution. They can try to find a veteran replacement who can win, a dicey proposition at best, or spend an inordinate amount of draft capital to trade up, hurting the rest of the roster. There also is the option of tanking a season in order to get back to the top of the draft. It can get you that high pick, but it leads to a miserable season first.
The situation the Cowboys wound up in 2015 has been termed "organic tanking". The failure of the backup quarterbacks to win more than one game without Romo has them picking fourth. That is good enough to get a franchise quarterback as long as there are more than one in this draft, since the Cleveland Browns are expected to take one of them ahead of the Cowboys. (Neither of the other two teams ahead of Dallas, the Tennessee Titans or the San Diego Chargers, are seen as likely to take a quarterback due to their current signal-callers.) This is why they should be willing to deviate from the "best player" approach. Even if a quarterback is not the highest player on their board when their turn in the draft comes, they should take him if they believe he is good enough to carry the team into the playoffs. If Romo is reasonably healthy this fall, they will not be picking near the start of the draft in 2017, and the opportunity will be gone.
Right now, there are two quarterbacks in this draft class that seem to be legitimate candidates to become NFL franchise quarterbacks, Jared Goff and Paxton Lynch. Which one is the best is a matter of opinion, depending on who is doing the evaluations, and those are likely to change as we go through the Combine and the rest of draft season. And there is something of a wild card in small school product Carson Wentz, who the Dallas coaching staff should be getting a long, hard look at during the Senior Bowl. And there also is the fact that the Browns have a history of taking the wrong quarterback anyway (see Brandon Weeden and Johnny Manziel). The best QB in the draft may not be gone just because they get first crack.
Of course, all this depends on how the Dallas scouts evaluate those three candidates (or perhaps some sleeper that they find outside of the names listed that they really believe in). Unless they truly believe a quarterback is capable of being a consistent winner as an NFL quarterback, they should not consider him for that fourth overall pick. But if they see the potential, especially factoring in that they should have a couple of years to work with a draftee before Romo is done, they should put aside other considerations and pull the trigger on taking that eventual replacement. Being in the top five in the draft is a rare situation for the Cowboys reccently, and it may not come again for a long time. Rather than take a lesser QB in the later rounds and hoping to get extremely lucky, they need to use the position they are in to maximize the chance of getting one with a much higher likelihood of success. They may not get another chance like this for years, and might have to suffer through another disaster like last season for that.
It will be costly to pass on a player that not only has All Pro potential and that could contribute immediately to take a quarterback that you don't want to see on the field for at least a couple of seasons, but QB is the one position that justifies electing that kind of long-term investment over instant payoff. We certainly did not want to go through the pain of 2015, but now that it is done, Dallas needs to capitalize on it. Quarterback is the most valuable resource in the NFL. The Cowboys have the draft capital to take one that could make the transition to the post-Romo years fairly painless. In most cases, a team should not commit to one position in the draft no matter who else is available. But in this case, that is exactly what Dallas should do. They can use the rest of the draft to strengthen other parts of the roster. If there is a real franchise quarterback available when they go on the clock with the fourth pick, they need to have the courage to take him.