There's a lot of optimisim and hyperbole about how good the Cowboys are. Improved defense (not much in my opinion), good draft (no doubt) but the schedule is going to be tough. When you finish 12-4, you get a tougher schedule. The defense is not going to be as good as most people here seem to think. Hardy's been out over a year, Gregory is a rookie, Jones is a rookie. Rookies don't normally perform well in their first year. Being out for over a year is going to impeded Hardy's effectiviness. Same goes for Lee. If the Cowboys can finish 4-4 the first 8 games then they'll be in a good spot. They should improve from that point on with Hardy getting more accustomed, Gregory and Jones getting a little experience. If they do any better than that then you'll know the this team is for real.
I never ever worry about the schedule. Teams change too much from year to year to really know what is or isn't a tough schedule.
McClain was good right away last year and he had been away from playing longer than Hardy has been. He was also a late addition that occured during TC; Hardy has had the entire offseason with the team. If a QB or WR missed a year I would be concerned, but a DL should get back up to speed in the preseason.
Gregory is just a bonus player at this point. Mincey and Lawrence will be the starters for game 1. Mincey averaged about a sack per game after he lost weight last season. Reports indicate he has kept his weight down this offseason.
Lee is the last guy that will take time to get up to speed. He studies football every day of the year according to other players and he will have given max effort to getting his knee right.
Sterling Moore was the 3rd CB most of the season. He has been replaced by Jones which should be a big upgrade.
The maturity of some young players is probably as big as the added players. Wilcox, Hitchens, and Lawrence should all be much further along than they were at the beginning of last year. Several other lower profile young players got some experience last season including two playoff games.
The depth has improved dramatically. Legit NFL players like Brinkley, Gachkar and Rivers will replace guys like Cam Lawrence and Keith Smith. Corey White as the 4th CB or 3rd Safety has a lot of experience for a young player. T. Crawford gets to start the season at DT instead of having to move from DE to DT like last season while having his weight down to 273. Hitchens was likely to replace RoMc in the Nickel anyway. They just need to replace RoMc in the base which is about 34% of the snaps.
They have a horde of options with young players on the DL. Improving over a gimpy Spencer and Selvie should not be difficult. Spencer did even play the first few games last year and DLaw was out half the season. It is highly likely that a couple of the lesser known guys step up. Bishop got NFL experience last year. Whaley and Gardner were redshirt type players last year.
If the defense is not significantly better then something went drastically wrong. Injuries are the only thing that could keep them from being significantly better. They have improved the depth so that should be a low probability.