Dline players are becoming more athletic and smaller but just as strong. Olines haven’t caught up
Well offensive lines won't catch up because there is something to be gained by defensive linemen to be smaller and agile...what is there to be gained by an offensive lineman by being small and agile?
Micah Parsons is 245 to 250 pounds. Would you try to block him with another man who was 245 to 250 pounds? Would you let your starting tight end block Parsons one on one for an entire game? Of course you wouldn't. You'd probably just try and find the biggest tallest strongest guy you got on your line and say well let's a least make it physically hard to shove this guy around every play. So you will never see a team draft or play the Micah Parsons of offensive linemen. Some guy who is between 240 and 250 pounds and has long arms and is a freak athlete, because high level athleticism doesn't come into play very often when your job is to either shove a man backwards or to keep from getting shoved backwards. You need big fat strong men for that.
Defensive lineman have to shoot the gap sometimes. That takes quickness. Offensive linemen don't.
Defensive lineman have to run twist and stunts that can require them to engage a blocker, stop, run around another man trying to get to the qb next to them, then run in a straight line to try and get to the qb. Offensive linemen don't do that. Most they are going to do is pull on a screen or run play. When was the last time, or the first time, you saw a guard, after the ball was snapped, switch places with a tackle to block a defender? When was the last time you saw a left guard run all the way to the right to block an outside linebacker, unless it was a run play or screen designed specifically for him to do that? You going to have a few plays a game where a defensive end tries to loop around like that on an obvious passing down.
Defensive lineman have to drop back in pass coverage sometimes. Sometimes they are out in space against running backs and receivers. Offensive linemen aren't doing that. Nobody is taking their nickel corners and just putting him over the guard to try and go at him 1 on 1.