Cooper's story is oddly similar to Williams. He started out as a wide receiver, but was moved to CB his senior year. He adapted amazingly well and was a seventh round pick by SF. He ran a 4.45 & 4.46 at the combine. He show well in preseason but was basically their last player cut. KC picked him up and he got a chance to play due injury. He was named their outstanding rookie and widely proclaimed to be a steal. He was was slated to start but nagging injuries and possibly some loss of confidence caused his performance to decline. Eventually the Chiefs tried him at corner but jumped at the chance to get something for him from the Cards.
He certainly is a temporary upgrade from Williams, but in the long run Williams has the potential to be better. Cooper still will have issues with fast receivers. That said his experience showed Sunday.