My purpose in mentioning the Petrobusians was simply to show that there were 'Protestants before the Reformation,' contra to your claims. There are others I could mention. You call them heretics; I call them martyrs. We both know who killed them.
Okay, so there were protestors (heretics) before the reformation. Yes, I knew that there were small sects of them sprinkled here and there, but we are still talking of a teaching that existed for some 1100 years regardless.
'"It is the Spirit who gives life; the flesh profits nothing" (John 6:63). In the sense that unbelievers understood Him, Christ says that the flesh profits nothing. His flesh bestows life in a different way, when it is received through the sacrament by those who have faith. Christ makes this clear by saying, "It is the Spirit who gives life." So in the sacrament, His body and blood have an effect which is spiritual in nature. The Spirit gives life, and without the Spirit's effect the sacraments feed the body but cannot feed the soul, which profits nothing. Here arises the question which many express when they say that these things do not happen symbolically but in reality. Those who say this are out of harmony with the writings of the holy fathers. Saint Augustine, the great teacher of the Church, writes in Book III of his work, On Christian Doctrine, as follows: "Unless you eat the flesh of the Son of Man, says the Saviour. and drink His blood, you shall not have life in you." Christ seems to be commanding a shameful crime [ie. cannibalism]. Therefore it is a symbol, requiring that we should faithfully remember that His flesh was crucified and wounded for us." We see that Augustine says that the sacraments of Christ's body and blood are celebrated in a symbolic sense by believers. For he says that to take Christ's flesh and blood in a fleshly sense involves crime, not religion.......
.........The Saviour and St. Paul teach us that the bread and wine placed on the altar are placed there as a symbol or memorial of the Lord's death [Luke 22:19; 1 Corinthians 11:24-25], so that what was done in the past may be called back to memory in the present. This is the purpose of the sacrament: through being made mindful of His sufferings, we are made sharers in that divine gift by which we have been liberated from death........'
[Ratramnus, Concerning Christ's body and Blood 2:31-34, 100-101, written 831 AD]
As late as the mid-11th Century, the question of Transubstantiation was still being debated between Berengar of Tours and Lanfranc of Canterbury. If memory serves, the doctrine did not become official Roman Catholic dogma until the Fourth Lateran Council in 1215.
And then we have these few quotes from the good St. Augustine from some of his sermons.
"That Bread which you see on the altar, having been sanctified by the word of God IS THE BODY OF CHRIST. That chalice, or rather, what is in that chalice, having been sanctified by the word of God, IS THE BLOOD OF CHRIST. Through that bread and wine the Lord Christ willed to commend HIS BODY AND BLOOD, WHICH HE POURED OUT FOR US UNTO THE FORGIVENESS OF SINS." (Sermons 227)
"The Lord Jesus wanted those whose eyes were held lest they should recognize him, to recognize Him in the breaking of the bread [Luke 24:16,30-35]. The faithful know what I am saying. They know Christ in the breaking of the bread. For not all bread, but only that which receives the blessing of Christ, BECOMES CHRIST'S BODY." (Sermons 234:2)
"What you see is the bread and the chalice; that is what your own eyes report to you. But what your faith obliges you to accept is that THE BREAD IS THE BODY OF CHRIST AND THE CHALICE [WINE] THE BLOOD OF CHRIST." (Sermons 272)
As for transubstantiation, it is an attempt by the Church to explain what Jesus proclaimed. It takes time to figure things out, years of study and this is what happened. The Eastern Orthodox Church which believes the same as we do concerning this issue makes no such attempt at explaining how this happens, they simply call it a mystery, but accepts that it indeed does happen as an article of faith.