It all comes down to how the current Cowboys offense has been built. Because Garrett's offense is so simplistic, it requires great individual talent on the OL and RB. That's why they had to spend three first rounders on Tyron, Frederick, and Martin. They were lucky to get Collins the way they did because he was probably a 1st round talent as well. Also, his offense is dependent on a GREAT RB, that's why it needs a workhorse like Demarco Murray or Zeke.
Unfortunately, this hasn't really been the winning formula for Super Bowl offenses in the last 10 years. SB teams don't usually spend so many resources on building the OL like that, they can manage to turn lesser-known players into serviceable starters. Same thing with RB - outside of Seattle and Marshawn, how many of the other recent SB winners had a great RB?
I'm not saying that drafting heavily on the OL and Zeke were bad moves - in fact, they were necessary for Garrett's offense. The problem is that due to Garrett's philosophy/scheme, we had to invest in those positions at the expense of defense over the last 7 years. Recent history shows that if your coaching/player development is worth a damn, you can win without a bunch of 1st rounders on the OL and a workhorse RB.
It's much easier to scheme to make average OL players into decent players. It's not as easy to do the same on defense...which seems to be the approach the Cowboys have taken. You spend the 1st round picks building your defense and then you can still win with the OL equivalents of the Benson Mayowas, Jack Crawfords, Terrell McClains, David Irvings, Tyrone Crawfords of the league. Instead, the Cowboys have done it backwards and now we have great individual talent on the OL that do not look so great vs. good defenses and mediocre talent on defense.