Khalid ibn al-Walid's absolute domination of the Sassanid empire during his Iraq campaign. How did this happen?

I recently watched this video- https://youtu.be/gCQAAI02qhc?si=RISpaUnc3PWHCmiV of khalib ibn-al walids conquest of Iraq in the Sassanid empire and was absolutely blown away by how brain dead, poorly lead, and how the Sasssanids employed such poor military tactics and strategy during this campaign. It was like they were tricked over and over in the most simple of ways and we're completely inept in the defense of their empire. How did this empire who went toe to toe with the Romans for hundreds of years seemingly completely fall apart and employ probably the worst defensive strategy I've ever seen an ancient military history?

Time and Time again they were led into the same trap and made the same mistakes. Their infamous horse archers and heavy cataphracts were nowhere to be found. They chose the absolute worst battlefields despite having the advantage many times of choosing the location of the battle. Is this video completely biased/one-sided or were Sassanids really that completely lost and pathetic during their campaign against the Muslim armies?