I don't think its exaggeration at all. If you start from their premise that "Catholicism is a false religion and all faith is built on "bible alone" then everything they postulate is built from those two axioms. In short the pillars of their faith are straw and stubble, not to mention being two legged, unstable.
The source does indeed matter. Were do you want to start, shall we start with the statement:
"Catholic divergence from the Bible on this most crucial of issues, salvation, means that yes, Catholicism is a false religion" since it is their pillar of their faith.
First, Catholicism does not diverge from Sacred Scripture, rather it the Church that give both authenticity and credibility to Sacred Scripture. Christ did not come to write a book, there is no evidence, though we are free to assume, that Christ could write.
Second, Sacred Scripture is the product of the Church and Scripture cannot be rightly understood outside the confines of the teachings of the Church. Sacred Scripture written by the Apostles for the authority of the Church to teach a divine Word divinely.
Read the Scripture within "the living Tradition of the whole Church". According to a saying of the Fathers,
Sacred Scripture is written principally in the Church's heart rather than in documents and records, for the Church carries in her Tradition the living memorial of God's Word, and it is the Holy Spirit who gives her the spiritual interpretation of the Scripture (". . . according to the spiritual meaning which the Spirit grants to the Church [
CCC 113]
Third, there are those who diverge from the Truth to support a god of their own making. Hence, they must always be in contention with Catholicism else, their subjective truth is revealed not to be reality. That is to say religions formed on this bases, such as Protestantism, reformism and Evangelicalism are all based on schism, a sin and a self delusional lie. Hence, they must find Catholicism to be false, else their schism is false. Reading Scripture in this way becomes unfruitful, the emotional juices might run deep but the pulp offer no nourishment to reason.
Fourth, it becomes evident to those who search truth that there is only on of such a thing, there cannot be a truth for the Baptist, another for the Methodist, Lutherans or any other "denomination" (a word derived from currency used to describe your faith). If it is true for the Baptist it must be true for the Methodist, Lutherans, and others, as well the Catholics. But, its not is it? In a comparison of any two only one can be true. If not then all are in error or only one is true and the others are false. Else, God is in error, which we know can't be true.
We have learned from none others the plan of our salvation, than from those through whom the gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith. ---Against Heresies III,1
When, however, they are confuted from the Scriptures, they turn round and accuse these same Scriptures, as if they were not correct, nor of authority, and [assert] that they are ambiguous, and that the truth cannot be extracted from them by those who are ignorant of tradition. ---Against Heresies III,2
Since we find that Sacred Scripture is the product of the Church, not the Church the product of a Book we are forced to concede Her supremacy in matters of doctrine and faith. The Holy Spirit guides her and her alone. And the Holy Spirit guides those outside the Church to truths residing in her treasury of faith and truth.
JosephT