Irenaeus taught in these books that if preaching is inconsistent with what is documented in the scriptures (both old and new) then one knows this is heresy. Simply put, if the Church is teaching things not in scripture (e.g. assumption of Mary, indulgences, etc.) then it is heresy. These examples are not listed in scripture nor were they taught by the Apostles. According to Irenaeus I should plug my ears and run.
As to Irenaeus saying the "truth is to be found nowhere else but in the Catholic Church", he was right....at the time he wrote that around 175-200 AD it was the ONLY place to hear the gospel. Based on his works and the way the Church has evolved, I sincerely doubt he would have used "Catholic" today.
Although at times he was obscure, and perhaps flawed in some of his reasoning, I was very impress with Irenaeus ability to use the Old and New Testaments. Irenaeus emphasized Joseph's role far more than Mary, telling us (correctly) that it was Joseph's responsibility for the caring and nurturing of Christ until adulthood and God the Father saddled the faithful Joseph with a great burden.
As far as not being able to find a "Protestant whole and complete in the entire history of the Church before the 1500s" you are incorrect. When I was researching the Reformation I went back to Augustine-not Calvin or Luther. Reading Irenaeus, although tedious (and dull at times) provides real insight into what exactly was meant by "tradition" and the great emphasis Irenaeus placed upon studying the scriptures. Today's Catholic Church has distorted the meaning of "tradition" to suit their only fancy and deemphasized the scriptures to the point where many Catholics no longer believe the Old Testament as well as parts of the New. I've discussed this with many Catholics on this site.
“As to Irenaeus saying the “truth is to be found nowhere else but in the Catholic Church”
First and foremost is this church today isn’t Catholic
“its roman catholic or church of rome” which ever you like.
The rcc is a counterfeit looks like the real deal, but with close inspection it’s found to be totally fake.