You're missing the forest for the trees. The objective of an offense isn't to complete as many deep passes as possible, it's to move the ball and score points. And that has nothing to do with how many yards we consider to be a "deep" pass. After trading for Cooper, this offense moved the ball but couldn't finish drives.
When you ignore the red zone, and instead call the deep ball the "fundamental problem" with the offense, you're putting more emphasis on something we need to do
more often than on the main thing that we
don't do well at all. The debate is yards vs. points. What difference does it make if we move up from 7th in yards to 3rd or 4th? Or from 2nd in TD scored from outside the red zone to 1st?
Maybe a point per game?
Offenses don't rely on 40+yard TD passes to score points, and no offense makes a living that way. Five teams led the NFL with 7 such plays last year. The Cowboys had 5 such plays, putting them in the
top 10. We had 8 TD passes of 30+ yards, which was also
top 10. And that's for the whole season, not just since Cooper's arrival.
Top 10 in yards (with Cooper), top 10 in long TD passes. Bottom 5 in the red zone.