This is the distinction between Total Depravity and Total Inability. But cooperating with God by virtue of preceding grace is not Semi-Pelagian. That's where you are wrong. If so, then Arminians are Semi-Pelagians, as well as Catholics and Orthodox. There is no need to go to the extreme lengths of asserting that man can do absolutely nothing with regard to his salvation.
Catholics usually go the other way.
The earlier something was taught, the more authority it is thought to hold. In general, though, it is obvious that when something is taught doesn't specifically have any bearing on whether it is true or not. I meant it only in the sense of developing knowledge in the Church, which we accept as a truism. In large part, because it had to respond to Monophysitism, a more subtle and sophisticated heresy than Arianism was. The teaching on justification and all the related issues had not been controversial before Luther.