My argument would be that if it weren't full, their seat would still have been available.

If you arrive at T-3, too bad. If you arrive at T-20, you're well within all the guidelines set out by AC.

The system once offloaded me for no apparent reason (I had a ~120 minute connection, but opted to board late because I had just a backpack), and they had upgraded someone into my seat. I was on the last flight of the night. The GA went on and downgraded them without any prodding on my part. So it can certainly be done.

That being said, I don't know if anything would be worth the fight if you already have a $200 voucher and it was only a one hour delay. Are you technically entitled to more.... possibly. But I'd probably leave it.