You wrote:
“Clearly it is. Augustine would not teach a Pelagian doctrine like the IC.”
So you believe being cleansed by Christ’s is Pelagian? Unbelievable.
No, I believe the IC is a Pelagian heresy. Among the ancient church, the only ones teaching a form of sinlessness were the Pelagians. None of the church fathers taught that Mary was immaculately conceived. So the claim of Ineffabilis Deus regarding the nature of this teaching in church history is basically a false one.