DL one yard off

Because they're "reading" something and then reacting to their read.

It is not at all unusual for some fronts to have a flex'd lineman.

That's what they do...read...react...flow.

Do you think you would adjust this tactic if you were playing a 1985 Pro I offense that runs ISO, trap, dive, off tackle, sweep, PAP?

I suppose...but the defense that drove the Pro 21 personnel off the field was either the Bear or the Double Eagle.  

3-0-3 with two 40 tech linebackers, a 6 tech and a ghost 6.  Two deep.  

Bear has two 40 tech's (LB and a Safety), 7 and a 9 tech linebackers with a single Safety.

If you wanted to flex, then the Desert Swarm defense did that.  They canted the NG into the Center and flex'd the weak-side 3 tech.

By doing that, both the flex and the LB could flow over the Center's block.

Facing those defenses, the Pro 21 offense had to spread out in order to survive.

They are not waiting and catching the OL a yard off the ball (or at least how we do it). It gives them a chance to be aggressive while being able to react to their read key. The DL is still firing off the ball and trying to re-establish the LOS if they are getting an attack read from their key, but not by just flying up field. We start off our DL about at this distance at the beginning, and tell them as they get stronger and better at reacting they can slowly inch closer. The closer you get the quicker your reaction time must be, and the stronger you must be cause you won't have as much momentum.
Also easier to do DL stunts with a little more depth.

The team has never played us off like this before. However, in the two previous meetings they have been more talented up front and as a whole defense.