The problem with something like Cal's Bear Raid in the NFL mostly comes down to the massive imbalance of talent between DL and OL. There are just far more talented defensive linemen than offensive linemen. This means a couple things:
NFL QB's don't have nearly as much time in the pocket as college QBs
More receivers = Fewer blockers, so it's easier for defenses to commit more to playing the pass
This translates to more 3-and-outs which, as we should be VERY familiar with after the last 5 years, translates to a tired defense and lots of losing.
See Chip Kelly's Eagles for an example of this.
McVay DOES like to "flood the field with pass catchers", as a recent article posted here stated. But one of the differences is his use of the TE position. The reason TE's are so valuable in today's NFL is because they create deception (run or pass?) with their blocking/catching ability, and mismatches in the secondary.
This is why, while guys like Kupp and Reynolds are exciting, we should be PRAYING that Everett, Higbee, and Hemingway turn out to be productive players. They are the key (along with Goff and the OL obviously) to our success.