Sure it is. It makes perfect sense from a statistical standpoint. We usually had 2 high safeties, and receivers were bracketed, so there was no one getting by us. The run game was more open in the short to medium range, but it is still in front of the defensive backs, so the likelihood of that being taken to the house is low.That's not a sound argument... It only takes one run to take it to the house as well. I see what you're saying, as long as we let the receivers get behind our DBs all the time, one and done... But they still have to execute it.
Bottom line is both ways are deadly... If we can't stop the run, we're in trouble. If we can't stop the pass, we're in trouble.
Pick your poison.
The idea is to lower the opposing teams odds of ultimate success by making them complete first down after first down, again and again to get down the field. Remember bend, don't break?
Under a man scheme there isn't as much help over the top if any at all, and if you get burned, it's going to be for 6 and it can happen right now.
So from a statistical standpoint, the two competing ideas can be viewed as 1) giving your defenses more chances to get a stop or the other 2) requiring your defense to be perfect (get burned once and it's a td, no other chances to stop them that drive cause the drive is over.)
Hopefully that helps explain the ideology behind it.